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The Effect Patterns Hub

A community-driven knowledge base of practical, goal-oriented patterns for building robust applications with Effect-TS.

This repository is designed to be a living document that helps developers move from core concepts to advanced architectural strategies by focusing on the "why" behind the code.

Looking for machine-readable rules for AI IDEs and coding agents? See the AI Coding Rules section below.

Table of Contents

Effect Patterns

• Getting Started
• Core Concepts
• Error Management
• Resource Management
• Concurrency
• Streams
• Schema
• Platform
• Scheduling
• Domain Modeling
• Building APIs
• Building Data Pipelines
• Making HTTP Requests
• Testing
• Observability
• Tooling and Debugging

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Getting Started

First steps with Effect - hello world, basic concepts

Pattern	Skill Level	Summary
Why Effect? Comparing Effect to Promise	🟢 Beginner	Understand what Effect gives you that Promise doesn't: type-safe errors, dependency injection, and composability.
Hello World: Your First Effect	🟢 Beginner	Create and run your very first Effect program using Effect.succeed and Effect.runSync.
Transform Values with Effect.map	🟢 Beginner	Use Effect.map to transform the success value of an Effect without changing its error or dependency types.
Handle Your First Error with Effect.fail and catchAll	🟢 Beginner	Learn how to create Effects that can fail and how to recover from those failures using Effect.fail and Effect.catchAll.
Run Multiple Effects in Parallel with Effect.all	🟢 Beginner	Use Effect.all to run multiple Effects at the same time and collect all their results.
Retry a Failed Operation with Effect.retry	🟢 Beginner	Use Effect.retry with a Schedule to automatically retry failed operations with customizable delays and limits.

Core Concepts

Fundamental Effect patterns - generators, pipes, dependencies

Pattern	Skill Level	Summary
Accumulate Multiple Errors with Either	🟢 Beginner	Use Either<E, A> to represent computations that can fail, allowing you to accumulate multiple errors instead of short-circuiting on the first one.
Chaining Computations with flatMap	🟢 Beginner	Use flatMap to chain together computations where each step may itself be effectful, optional, or error-prone.
Combining Values with zip	🟢 Beginner	Use zip to combine two computations, pairing their results together in Effect, Stream, Option, or Either.
Comparing Data by Value with Data.struct	🟢 Beginner	Use Data.struct to create immutable, structurally-typed objects that can be compared by value, not by reference.
Comparing Data by Value with Structural Equality	🟢 Beginner	Use Data.struct and Equal.equals to safely compare objects by their value instead of their reference, avoiding common JavaScript pitfalls.
Conditional Branching with if, when, and cond	🟢 Beginner	Use combinators like if, when, and cond to express conditional logic declaratively across Effect, Stream, Option, and Either.
Converting from Nullable, Option, or Either	🟢 Beginner	Use fromNullable, fromOption, and fromEither to convert nullable values, Option, or Either into Effects or Streams, enabling safe and composable interop.
Create Pre-resolved Effects with succeed and fail	🟢 Beginner	Use Effect.succeed(value) to create an Effect that immediately succeeds with a value, and Effect.fail(error) for an Effect that immediately fails.
Creating from Collections	🟢 Beginner	Use fromIterable and fromArray to create Streams or Effects from arrays, iterables, or other collections, enabling batch and streaming operations.
Creating from Synchronous and Callback Code	🟢 Beginner	Use sync and async to lift synchronous or callback-based computations into Effect, enabling safe and composable interop with legacy code.
Execute Asynchronous Effects with Effect.runPromise	🟢 Beginner	Use Effect.runPromise at the 'end of the world' to execute an asynchronous Effect and get its result as a JavaScript Promise.
Execute Synchronous Effects with Effect.runSync	🟢 Beginner	Use Effect.runSync at the 'end of the world' to execute a purely synchronous Effect and get its value directly.
Filtering Results with filter	🟢 Beginner	Use filter to keep or discard results based on a predicate, across Effect, Stream, Option, and Either.
Lifting Errors and Absence with fail, none, and left	🟢 Beginner	Use fail, none, and left to represent errors or absence in Effect, Option, or Either, making failures explicit and type-safe.
Lifting Values with succeed, some, and right	🟢 Beginner	Use succeed, some, and right to lift plain values into Effect, Option, or Either, making them composable and type-safe.
Model Optional Values Safely with Option	🟢 Beginner	Use Option to explicitly represent a value that may or may not exist, eliminating null and undefined errors.
Set Up a New Effect Project	🟢 Beginner	Initialize a new Node.js project with the necessary TypeScript configuration and Effect dependencies to start building.
Solve Promise Problems with Effect	🟢 Beginner	Understand how Effect solves the fundamental problems of native Promises, such as untyped errors, lack of dependency injection, and no built-in cancellation.
Transform Effect Values with map and flatMap	🟢 Beginner	Use Effect.map for synchronous transformations and Effect.flatMap to chain operations that return another Effect.
Transforming Values with map	🟢 Beginner	Use map to transform the result of an Effect, Stream, Option, or Either in a declarative, type-safe way.
Understand that Effects are Lazy Blueprints	🟢 Beginner	An Effect is a lazy, immutable blueprint describing a computation, which does nothing until it is explicitly executed by a runtime.
Understand the Three Effect Channels (A, E, R)	🟢 Beginner	Learn about the three generic parameters of an Effect: the success value (A), the failure error (E), and the context requirements (R).
Use .pipe for Composition	🟢 Beginner	Use the .pipe() method to chain multiple operations onto an Effect in a readable, top-to-bottom sequence.
Working with Immutable Arrays using Data.array	🟢 Beginner	Use Data.array to create immutable, type-safe arrays that support value-based equality and safe functional operations.
Working with Tuples using Data.tuple	🟢 Beginner	Use Data.tuple to create immutable, type-safe tuples that support value-based equality and pattern matching.
Wrap Asynchronous Computations with tryPromise	🟢 Beginner	Use Effect.tryPromise to safely convert a function that returns a Promise into an Effect, capturing rejections in the error channel.
Wrap Synchronous Computations with sync and try	🟢 Beginner	Use Effect.sync for non-throwing synchronous code and Effect.try for synchronous code that might throw an exception.
Wrapping Synchronous and Asynchronous Computations	🟢 Beginner	Use try and tryPromise to safely wrap synchronous or asynchronous computations that may throw or reject, capturing errors in the Effect world.
Write Sequential Code with Effect.gen	🟢 Beginner	Use Effect.gen with yield* to write sequential, asynchronous code in a style that looks and feels like familiar async/await.
Access Configuration from the Context	🟡 Intermediate	Access your type-safe configuration within an Effect.gen block by yielding the Config object you defined.
Beyond the Date Type - Real World Dates, Times, and Timezones	🟡 Intermediate	Use the Clock service for testable access to the current time and prefer immutable primitives for storing and passing timestamps.
Control Flow with Conditional Combinators	🟡 Intermediate	Use combinators like Effect.if, Effect.when, and Effect.cond to handle conditional logic in a declarative, composable way.
Define a Type-Safe Configuration Schema	🟡 Intermediate	Use Effect.Config primitives to define a schema for your application's configuration, ensuring type-safety and separation from code.
Handling Errors with catchAll, orElse, and match	🟡 Intermediate	Use catchAll, orElse, and match to recover from errors, provide fallbacks, or transform errors in Effect, Either, and Option.
Manage Shared State Safely with Ref	🟡 Intermediate	Use Ref to model shared, mutable state in a concurrent environment, ensuring all updates are atomic and free of race conditions.
Mapping and Chaining over Collections with forEach and all	🟡 Intermediate	Use forEach and all to apply effectful functions to collections and combine the results, enabling batch and parallel processing.
Modeling Effect Results with Exit	🟡 Intermediate	Use Exit<E, A> to represent the result of running an Effect, capturing both success and failure (including defects) in a type-safe way.
Modeling Tagged Unions with Data.case	🟡 Intermediate	Use Data.case to create tagged unions (algebraic data types) for robust, type-safe domain modeling and pattern matching.
Optional Pattern 1: Handling None and Some Values	🟡 Intermediate	Use Effect's Option type to safely handle values that may not exist, avoiding null/undefined bugs and enabling composable error handling.
Process Streaming Data with Stream	🟡 Intermediate	Use Stream<A, E, R> to represent and process data that arrives over time, such as file reads, WebSocket messages, or paginated API results.
Provide Configuration to Your App via a Layer	🟡 Intermediate	Use Config.layer(schema) to create a Layer that provides your configuration schema to the application's context.
Redact and Handle Sensitive Data	🟡 Intermediate	Use Redacted to securely handle sensitive data, ensuring secrets are not accidentally logged or exposed.
Representing Time Spans with Duration	🟡 Intermediate	Use Duration to represent time intervals in a type-safe, human-readable, and composable way.
Representing Time Spans with Duration	🟡 Intermediate	Use the Duration data type to represent time intervals in a type-safe, human-readable, and composable way.
Sequencing with andThen, tap, and flatten	🟡 Intermediate	Use andThen, tap, and flatten to sequence computations, run side effects, and flatten nested structures in Effect, Stream, Option, and Either.
Type Classes for Equality, Ordering, and Hashing with Data.Class	🟡 Intermediate	Use Data.Class to derive and implement type classes for equality, ordering, and hashing, enabling composable and type-safe abstractions.
Understand Layers for Dependency Injection	🟡 Intermediate	A Layer is a blueprint that describes how to build a service, detailing its own requirements and any potential errors during its construction.
Use Chunk for High-Performance Collections	🟡 Intermediate	Use Chunk as a high-performance, immutable alternative to JavaScript's Array, especially for data processing pipelines.
Use Chunk for High-Performance Collections	🟡 Intermediate	Use Chunk as a high-performance, immutable alternative to JavaScript's Array, especially for data processing pipelines.
Work with Arbitrary-Precision Numbers using BigDecimal	🟡 Intermediate	Use BigDecimal for arbitrary-precision decimal arithmetic, avoiding rounding errors and loss of precision in financial or scientific calculations.
Work with Dates and Times using DateTime	🟡 Intermediate	Use DateTime for immutable, time-zone-aware date and time values, enabling safe and precise time calculations.
Work with Immutable Sets using HashSet	🟡 Intermediate	Use HashSet to model immutable, high-performance sets for efficient membership checks and set operations.
Create a Reusable Runtime from Layers	🟠 Advanced	Compile your application's layers into a reusable Runtime object to efficiently execute multiple effects that share the same context.
Handle Unexpected Errors by Inspecting the Cause	🟠 Advanced	Use Cause to get rich, structured information about errors and failures, including defects, interruptions, and error traces.
Optional Pattern 2: Optional Chaining and Composition	🟠 Advanced	Chain optional values across multiple steps with composable operators, enabling elegant data flow through systems with missing values.

Error Management

Handle errors, create typed errors, recovery strategies

Pattern	Skill Level	Summary
Checking Option and Either Cases	🟢 Beginner	Use isSome, isNone, isLeft, and isRight to check Option and Either cases for simple, type-safe branching.
Matching on Success and Failure with match	🟢 Beginner	Use match to handle both success and failure cases in a single, declarative place for Effect, Option, and Either.
Pattern Match on Option and Either	🟢 Beginner	Use declarative match() combinators to handle optional and error-prone values
Your First Error Handler	🟢 Beginner	Learn the basics of handling errors in Effect with catchAll and catchTag.
Conditionally Branching Workflows	🟡 Intermediate	Use predicate-based operators like Effect.filter and Effect.if to make decisions and control the flow of your application based on runtime values.
Control Repetition with Schedule	🟡 Intermediate	Use Schedule to create composable, stateful policies that define precisely how an effect should be repeated or retried.
Effectful Pattern Matching with matchEffect	🟡 Intermediate	Use matchEffect to perform effectful branching based on success or failure, enabling rich workflows in the Effect world.
Error Handling Pattern 1: Accumulating Multiple Errors	🟡 Intermediate	Collect multiple errors across operations instead of failing on first error, enabling comprehensive error reporting and validation.
Handle Errors with catchTag, catchTags, and catchAll	🟡 Intermediate	Use catchTag for type-safe recovery from specific tagged errors, and catchAll to recover from any possible failure.
Handle Flaky Operations with Retries and Timeouts	🟡 Intermediate	Use Effect.retry and Effect.timeout to build resilience against slow or intermittently failing operations, such as network requests.
Handling Specific Errors with catchTag and catchTags	🟡 Intermediate	Use catchTag and catchTags to recover from or handle specific error types in the Effect failure channel, enabling precise and type-safe error recovery.
Leverage Effect's Built-in Structured Logging	🟡 Intermediate	Use Effect's built-in logging functions (Effect.log, Effect.logInfo, etc.) for structured, configurable, and context-aware logging.
Mapping Errors to Fit Your Domain	🟡 Intermediate	Use Effect.mapError to transform specific, low-level errors into more general domain errors, creating clean architectural boundaries.
Matching Tagged Unions with matchTag and matchTags	🟡 Intermediate	Use matchTag and matchTags to pattern match on specific tagged union cases, enabling precise and type-safe branching.
Retry Operations Based on Specific Errors	🟡 Intermediate	Use Effect.retry and predicate functions to selectively retry an operation only when specific, recoverable errors occur.
Scheduling Pattern 2: Implement Exponential Backoff for Retries	🟡 Intermediate	Use exponential backoff with jitter to retry failed operations with increasing delays, preventing resource exhaustion and cascade failures in distributed systems.
Error Handling Pattern 2: Error Propagation and Chains	🟠 Advanced	Propagate errors through effect chains with context, preserving error information and enabling recovery at appropriate layers.
Error Handling Pattern 3: Custom Error Strategies	🟠 Advanced	Build domain-specific error types and recovery strategies that align with business logic and provide actionable error information.
Handle Unexpected Errors by Inspecting the Cause	🟠 Advanced	Use Effect.catchAllCause or Effect.runFork to inspect the Cause of a failure, distinguishing between expected errors (Fail) and unexpected defects (Die).

Resource Management

Acquire and release resources safely with Scope

Pattern	Skill Level	Summary
Safely Bracket Resource Usage with acquireRelease	🟢 Beginner	Use Effect.acquireRelease to guarantee a resource's cleanup logic runs, even if errors or interruptions occur.
Compose Resource Lifecycles with Layer.merge	🟡 Intermediate	Combine multiple resource-managing layers, letting Effect automatically handle the acquisition and release order.
Create a Service Layer from a Managed Resource	🟡 Intermediate	Use Layer.scoped with Effect.Service to transform a managed resource into a shareable, application-wide service.
Handle Resource Timeouts	🟡 Intermediate	Set timeouts on resource acquisition and usage to prevent hanging operations.
Pool Resources for Reuse	🟡 Intermediate	Create and manage a pool of reusable resources like database connections or workers.
Create a Managed Runtime for Scoped Resources	🟠 Advanced	Use Layer.launch to safely manage the lifecycle of layers containing scoped resources, ensuring finalizers are always run.
Manage Hierarchical Resources	🟠 Advanced	Manage parent-child resource relationships where children must be released before parents.
Manually Manage Lifecycles with Scope	🟠 Advanced	Use Scope directly to manage complex resource lifecycles or when building custom layers.

Concurrency

Run effects in parallel, manage fibers, coordinate async work

Pattern	Skill Level	Summary
Concurrency Pattern 1: Coordinate Async Operations with Deferred	🟡 Intermediate	Use Deferred to coordinate async operations where multiple fibers wait for a single event to complete, enabling producer-consumer patterns and async signaling without polling.
Concurrency Pattern 2: Rate Limit Concurrent Access with Semaphore	🟡 Intermediate	Use Semaphore to limit the number of concurrent operations, enabling connection pooling, API rate limiting, and controlled resource access without overload.
Concurrency Pattern 3: Coordinate Multiple Fibers with Latch	🟡 Intermediate	Use Latch to synchronize multiple fibers, enabling patterns like coordinating N async tasks, fan-out/fan-in, and barrier synchronization.
Concurrency Pattern 4: Distribute Work with Queue	🟡 Intermediate	Use Queue to decouple producers and consumers, enabling work distribution, pipeline stages, and backpressure handling across concurrent fibers.
Concurrency Pattern 5: Broadcast Events with PubSub	🟡 Intermediate	Use PubSub to broadcast events to multiple subscribers, enabling event-driven architectures and fan-out patterns without direct coupling.
Concurrency Pattern 6: Race and Timeout Competing Effects	🟡 Intermediate	Use race and timeout to compete multiple effects and enforce deadlines, enabling timeout handling and choosing fastest result.
Manage Shared State Safely with Ref	🟡 Intermediate	Use Ref to model shared, mutable state in a concurrent environment, ensuring all updates are atomic and free of race conditions.
Process a Collection in Parallel with Effect.forEach	🟡 Intermediate	Use Effect.forEach with the concurrency option to process a collection of items in parallel with a fixed limit, preventing resource exhaustion.
Race Concurrent Effects for the Fastest Result	🟡 Intermediate	Use Effect.race to run multiple effects concurrently and proceed with the result of the one that succeeds first, automatically interrupting the others.
Run Independent Effects in Parallel with Effect.all	🟡 Intermediate	Use Effect.all to run multiple independent effects concurrently and collect all their results into a single tuple.
Add Caching by Wrapping a Layer	🟠 Advanced	Implement caching by creating a new layer that wraps a live service, intercepting method calls to add caching logic without modifying the original service.
Decouple Fibers with Queues and PubSub	🟠 Advanced	Use Queue for point-to-point work distribution and PubSub for broadcast messaging to enable safe, decoupled communication between concurrent fibers.
Execute Long-Running Apps with Effect.runFork	🟠 Advanced	Use Effect.runFork at the application's entry point to launch a long-running process as a detached fiber, allowing for graceful shutdown.
Implement Graceful Shutdown for Your Application	🟠 Advanced	Use Effect.runFork and listen for OS signals (SIGINT, SIGTERM) to trigger a Fiber.interrupt, ensuring all resources are safely released.
Manage Resource Lifecycles with Scope	🟠 Advanced	Use Scope for fine-grained, manual control over resource lifecycles, ensuring cleanup logic (finalizers) is always executed.
Poll for Status Until a Task Completes	🟠 Advanced	Use Effect.race to run a repeating polling effect alongside a main task, automatically stopping the polling when the main task finishes.
Run Background Tasks with Effect.fork	🟠 Advanced	Use Effect.fork to start a computation in a background fiber, allowing the parent fiber to continue its work without waiting.
State Management Pattern 1: Synchronized Reference with SynchronizedRef	🟠 Advanced	Use SynchronizedRef to safely share mutable state across concurrent fibers, with atomic updates and guaranteed consistency.
State Management Pattern 2: Observable State with SubscriptionRef	🟠 Advanced	Build observable state that notifies subscribers on changes, enabling reactive patterns and state-driven architecture.
Understand Fibers as Lightweight Threads	🟠 Advanced	A Fiber is a lightweight, virtual thread managed by the Effect runtime, enabling massive concurrency on a single OS thread without the overhead of traditional threading.

Getting Started

Pattern	Skill Level	Summary
Race Effects and Handle Timeouts	🟢 Beginner	Race multiple effects to get the fastest result, or add timeouts to prevent hanging operations.
Understanding Fibers	🟢 Beginner	Learn what fibers are, how they differ from threads, and why they make Effect powerful for concurrent programming.
Your First Parallel Operation	🟢 Beginner	Run multiple effects in parallel with Effect.all and understand when to use parallel vs sequential execution.
undefined	🟡 Intermediate

Streams

Process sequences of data with Stream

Pattern	Skill Level	Summary
Stream Pattern 1: Transform Streams with Map and Filter	🟢 Beginner	Use Stream.map and Stream.filter to transform and select stream elements, enabling data pipelines that reshape and filter data in flight.
Stream Pattern 2: Merge and Combine Multiple Streams	🟡 Intermediate	Use Stream.merge, Stream.concat, and Stream.mergeAll to combine multiple streams into a single stream, enabling multi-source data aggregation.
Stream Pattern 3: Control Backpressure in Streams	🟡 Intermediate	Use Stream throttling, buffering, and chunk operations to manage backpressure, preventing upstream from overwhelming downstream consumers.
Stream Pattern 4: Stateful Operations with Scan and Fold	🟡 Intermediate	Use Stream.scan and Stream.fold to maintain state across stream elements, enabling cumulative operations, counters, aggregations, and stateful transformations.
Stream Pattern 5: Grouping and Windowing Streams	🟠 Advanced	Use grouping and windowing to organize streams by key or time window, enabling batch operations and temporal aggregations.
Stream Pattern 6: Resource Management in Streams	🟠 Advanced	Properly manage resources (connections, files, memory) in streams using acquire/release patterns and ensuring cleanup on error or completion.
Stream Pattern 7: Error Handling in Streams	🟠 Advanced	Handle errors gracefully in streams with recovery strategies, resuming after failures, and maintaining stream integrity.
Stream Pattern 8: Advanced Stream Transformations	🟠 Advanced	Apply complex transformations across streams including custom operators, effect-based transformations, and composition patterns.

Getting Started

Pattern	Skill Level	Summary
Running and Collecting Stream Results	🟢 Beginner	Learn the different ways to run a stream and collect its results: runCollect, runForEach, runDrain, and more.
Stream vs Effect - When to Use Which	🟢 Beginner	Understand when to use Effect (single value) vs Stream (sequence of values) for your use case.
Take and Drop Stream Elements	🟢 Beginner	Control how many stream elements to process using take, drop, takeWhile, and dropWhile.
Your First Stream	🟢 Beginner	Create your first Effect Stream and understand what makes streams different from regular arrays.

Sinks

Pattern	Skill Level	Summary
Sink Pattern 1: Batch Insert Stream Records into Database	🟡 Intermediate	Use Sink to batch stream records and insert them efficiently into a database in groups, rather than one-by-one, for better performance and resource usage.
Sink Pattern 2: Write Stream Events to Event Log	🟡 Intermediate	Use Sink to append stream events to an event log with metadata and causal ordering, enabling event sourcing and audit trail patterns.
Sink Pattern 3: Write Stream Lines to File	🟡 Intermediate	Use Sink to write stream data as lines to a file with buffering for efficiency, supporting log files and line-oriented formats.
Sink Pattern 4: Send Stream Records to Message Queue	🟡 Intermediate	Use Sink to publish stream records to a message queue with partitioning, batching, and acknowledgment handling for distributed systems.
Sink Pattern 5: Fall Back to Alternative Sink on Failure	🟡 Intermediate	Use Sink to attempt writing to a primary destination, and automatically fall back to an alternative destination if the primary fails, enabling progressive degradation and high availability.
Sink Pattern 6: Retry Failed Stream Operations	🟡 Intermediate	Use Sink with configurable retry policies to automatically retry failed operations with exponential backoff, enabling recovery from transient failures without losing data.

Schema

Validate and transform data with Effect Schema

Getting Started

Pattern	Skill Level	Summary
Decode and Encode Data	🟢 Beginner
Effect Schema vs Zod	🟢 Beginner
Handling Parse Errors	🟢 Beginner
Your First Schema	🟢 Beginner

Ai Schemas

Pattern	Skill Level	Summary
Adding Descriptions for AI Context	🟢 Beginner
Basic AI Output Schema	🟢 Beginner
Basic AI Response Parsing	🟢 Beginner
Handling Malformed AI Outputs	🟢 Beginner
Enums and Literal Types	🟡 Intermediate
Nested Object Schemas	🟡 Intermediate
Parsing Partial/Incomplete Responses	🟡 Intermediate
Retry Strategies for Parse Failures	🟡 Intermediate
Union Types for Flexible Outputs	🟡 Intermediate
Integration with Vercel AI SDK	🟠 Advanced
Validating Streaming AI Responses	🟠 Advanced

Arrays

Pattern	Skill Level	Summary
Array Validation	🟢 Beginner
Tuple Schemas	🟢 Beginner

Async Validation

Pattern	Skill Level	Summary
Basic Async Validation with Schema.filterEffect	🟢 Beginner
Database Validation - Uniqueness, Foreign Keys, Constraints	🟡 Intermediate
External API Validation During Schema Parsing	🟡 Intermediate
Efficient Batched Async Validation and Deduplication	🟠 Advanced

Composition

Pattern	Skill Level	Summary
Extending and Adding Fields to Schemas	🟢 Beginner
Merging Multiple Schemas into One	🟡 Intermediate
Pick and Omit - Selecting and Excluding Fields	🟡 Intermediate
Schema Inheritance and Specialization	🟡 Intermediate

Environment Config

Pattern	Skill Level	Summary
Environment Variables with Schema Validation	🟢 Beginner
Composable Configuration Layers	🟡 Intermediate
Feature Flags with Dynamic Validation	🟡 Intermediate
Secrets Redaction and Masking	🟡 Intermediate

Error Handling

Pattern	Skill Level	Summary
Custom Tagged Errors	🟢 Beginner
Error Aggregation and Collection	🟡 Intermediate
Error Recovery and Fallback Strategies	🟡 Intermediate
User-Friendly Error Messages	🟡 Intermediate

Form Validation

Pattern	Skill Level	Summary
Basic Form Validation	🟢 Beginner
Collecting All Validation Errors	🟢 Beginner
Async Validation (Username Availability)	🟡 Intermediate
Dependent Field Validation	🟡 Intermediate
Nested Form Structures	🟡 Intermediate

Json Validation

Pattern	Skill Level	Summary
Basic JSON File Validation	🟢 Beginner
Validating Config Files	🟢 Beginner
Validating JSON Database Columns	🟢 Beginner
Handling Schema Evolution	🟡 Intermediate
PostgreSQL JSONB Validation	🟡 Intermediate
Schema with Default Values	🟡 Intermediate
Validating Multiple Config Files	🟡 Intermediate
Validating Partial Documents	🟡 Intermediate

Objects

Pattern	Skill Level	Summary
Basic Object Schemas	🟢 Beginner
Nested Object Schemas	🟢 Beginner
Optional and Nullable Fields	🟢 Beginner

Primitives

Pattern	Skill Level	Summary
Date Validation and Parsing	🟢 Beginner
Enums and Literal Types	🟢 Beginner
Number Validation and Refinements	🟢 Beginner
String Validation and Refinements	🟢 Beginner

Recursive

Pattern	Skill Level	Summary
Basic Recursive Schemas with Schema.suspend	🟢 Beginner
Nested Comments and Threaded Discussions	🟡 Intermediate
Tree Structures - File Systems, Org Charts, Hierarchies	🟡 Intermediate
Parsing JSON into Typed Abstract Syntax Trees	🟠 Advanced

Transformations

Pattern	Skill Level	Summary
Basic Schema Transformations	🟢 Beginner
Bidirectional API ↔ Domain ↔ DB Transformations	🟡 Intermediate
Branded Types for Type-Safe IDs and Strings	🟡 Intermediate
Data Normalization and Canonical Forms	🟡 Intermediate

Unions

Pattern	Skill Level	Summary
Basic Union Types and Alternatives	🟢 Beginner
Discriminated Unions with Type Narrowing	🟡 Intermediate
Exhaustive Pattern Matching and Never Types	🟡 Intermediate
Polymorphic API Responses and Data Shaping	🟡 Intermediate

Validating Api Responses

Pattern	Skill Level	Summary
Basic API Response Decoding	🟢 Beginner
Handling Decode Failures	🟢 Beginner
API Validation with Retry	🟡 Intermediate
Decoding Nested API Responses	🟡 Intermediate
Handling Union/Discriminated Responses	🟡 Intermediate
Full Pipeline with @effect/platform	🟠 Advanced

Web Standards Validation

Pattern	Skill Level	Summary
Email Address Validation	🟢 Beginner
URL Validation	🟢 Beginner
UUID Validation (v4, v7)	🟢 Beginner
HTTP Header Validation	🟡 Intermediate
ISO 8601 Date Validation	🟡 Intermediate
MIME Type Validation	🟡 Intermediate

Platform

System operations - files, commands, environment

Pattern	Skill Level	Summary
Platform Pattern 2: Filesystem Operations	🟢 Beginner	Use FileSystem module to read, write, list, and manage files with proper resource cleanup and error handling.
Platform Pattern 4: Interactive Terminal I/O	🟢 Beginner	Use Terminal module to read user input and write formatted output, enabling interactive CLI applications with proper buffering and encoding.
Platform Pattern 1: Execute Shell Commands	🟡 Intermediate	Use Command module to execute shell commands, capture output, and handle exit codes, enabling integration with system tools and external programs.
Platform Pattern 3: Persistent Key-Value Storage	🟡 Intermediate	Use KeyValueStore for simple persistent key-value storage, enabling caching, session management, and lightweight data persistence.
Platform Pattern 5: Cross-Platform Path Manipulation	🟡 Intermediate	Use platform-aware path operations to handle file system paths correctly across Windows, macOS, and Linux with proper resolution and normalization.
Platform Pattern 6: Advanced FileSystem Operations	🟠 Advanced	Handle complex file system scenarios including watching files, recursive operations, atomic writes, and efficient bulk operations.

Getting Started

Pattern	Skill Level	Summary
Access Environment Variables	🟢 Beginner	Read environment variables safely with Effect Platform, handling missing values gracefully.
Your First Platform Operation	🟢 Beginner	Get started with Effect Platform by reading a file and understanding how Platform differs from Node.js APIs.

Scheduling

Schedule and repeat effects with Schedule

Pattern	Skill Level	Summary
Retry Failed Operations	🟢 Beginner	Use Effect.retry with Schedule to automatically retry operations that fail.
Your First Schedule	🟢 Beginner	Learn the basics of scheduling in Effect - retry operations and repeat them on intervals.
Scheduling Pattern 1: Repeat an Effect on a Fixed Interval	🟡 Intermediate	Use Schedule.fixed to repeat an effect at regular intervals, enabling polling, health checks, and periodic background tasks without busy-waiting or manual timing logic.
Scheduling Pattern 3: Schedule Tasks with Cron Expressions	🟡 Intermediate	Use cron expressions to schedule tasks at specific times and intervals, enabling calendar-based scheduling with timezone support.
Scheduling Pattern 4: Debounce and Throttle Execution	🟡 Intermediate	Use debouncing and throttling to limit how often effects execute, preventing runaway operations and handling rapid event sequences.
Scheduling Pattern 5: Advanced Retry Chains and Circuit Breakers	🟠 Advanced	Build sophisticated retry chains with circuit breakers, fallbacks, and complex failure patterns for production-grade reliability.

Domain Modeling

Model business domains with branded types and services

Pattern	Skill Level	Summary
Create Type-Safe Errors	🟢 Beginner	Define domain-specific errors using Data.TaggedError for type-safe error handling.
Handle Missing Values with Option	🟢 Beginner	Use Option to explicitly model values that might not exist, avoiding null/undefined bugs.
Your First Domain Model	🟢 Beginner	Create a simple domain model using TypeScript interfaces and Effect to represent your business entities.
Accumulate Multiple Errors with Either	🟡 Intermediate	Use Either<E, A> to represent computations that can fail, allowing you to accumulate multiple errors instead of short-circuiting on the first one.
Avoid Long Chains of .andThen; Use Generators Instead	🟡 Intermediate	Prefer Effect.gen over long chains of .andThen for sequential logic to improve readability and maintainability.
Define Contracts Upfront with Schema	🟡 Intermediate	Use Schema to define the types for your data models and function signatures before writing the implementation, creating clear, type-safe contracts.
Define Type-Safe Errors with Data.TaggedError	🟡 Intermediate	Create custom, type-safe error classes by extending Data.TaggedError to make error handling robust, predictable, and self-documenting.
Distinguish 'Not Found' from Errors	🟡 Intermediate	Use Effect<Option> to clearly distinguish between a recoverable 'not found' case (None) and a true failure (Fail).
Model Optional Values Safely with Option	🟡 Intermediate	Use Option to explicitly represent a value that may or may not exist, eliminating null and undefined errors.
Model Validated Domain Types with Brand	🟡 Intermediate	Use Brand to turn primitive types like string or number into specific, validated domain types like Email or PositiveInt, making illegal states unrepresentable.
Modeling Validated Domain Types with Brand	🟡 Intermediate	Use Brand to create domain-specific types from primitives, making illegal states unrepresentable and preventing accidental misuse.
Parse and Validate Data with Schema.decode	🟡 Intermediate	Use Schema.decode(schema) to create an Effect that parses and validates unknown data, which integrates seamlessly with Effect's error handling.
Transform Data During Validation with Schema	🟡 Intermediate	Use Schema.transform to safely convert data from one type to another during the parsing phase, such as from a string to a Date.
Use Effect.gen for Business Logic	🟡 Intermediate	Encapsulate sequential business logic, control flow, and dependency access within Effect.gen for improved readability and maintainability.
Validating and Parsing Branded Types	🟡 Intermediate	Use Schema and Brand together to validate and parse branded types at runtime, ensuring only valid values are constructed.

Building APIs

Build HTTP APIs and services

Pattern	Skill Level	Summary
Create a Basic HTTP Server	🟢 Beginner	Launch a simple, effect-native HTTP server to respond to incoming requests.
Extract Path Parameters	🟢 Beginner	Capture and use dynamic segments from a request URL, such as a resource ID.
Handle a GET Request	🟢 Beginner	Define a route that responds to a specific HTTP GET request path.
Send a JSON Response	🟢 Beginner	Create and send a structured JSON response with the correct headers and status code.
Add Rate Limiting to APIs	🟡 Intermediate	Protect your API from abuse by limiting request rates per client.
Compose API Middleware	🟡 Intermediate	Build reusable middleware for logging, authentication, validation, and more.
Configure CORS for APIs	🟡 Intermediate	Enable Cross-Origin Resource Sharing to allow browser clients from different domains.
Handle API Errors	🟡 Intermediate	Translate application-specific errors from the Effect failure channel into meaningful HTTP error responses.
Implement API Authentication	🟡 Intermediate	Add JWT or session-based authentication to protect your API endpoints.
Make an Outgoing HTTP Client Request	🟡 Intermediate	Use the built-in Effect HTTP client to make safe and composable requests to external services from within your API.
Provide Dependencies to Routes	🟡 Intermediate	Inject services like database connections into HTTP route handlers using Layer and Effect.Service.
Validate Request Body	🟡 Intermediate	Safely parse and validate an incoming JSON request body against a predefined Schema.
Generate OpenAPI Documentation	🟠 Advanced	Auto-generate OpenAPI/Swagger documentation from your Effect HTTP API definitions.

Building Data Pipelines

Process and transform data at scale

Pattern	Skill Level	Summary
Collect All Results into a List	🟢 Beginner	Run a pipeline and gather all of its results into an in-memory array.
Create a Stream from a List	🟢 Beginner	Turn a simple in-memory array or list into a foundational data pipeline using Stream.
Run a Pipeline for its Side Effects	🟢 Beginner	Execute a pipeline for its effects without collecting the results, saving memory.
Automatically Retry Failed Operations	🟡 Intermediate	Build a self-healing pipeline that can automatically retry failed processing steps using a configurable backoff strategy.
Merge Multiple Streams	🟡 Intermediate	Combine data from multiple streams into a single unified stream.
Process a Large File with Constant Memory	🟡 Intermediate	Create a data pipeline from a file on disk, processing it line-by-line without loading the entire file into memory.
Process collections of data asynchronously	🟡 Intermediate	Process collections of data asynchronously in a lazy, composable, and resource-safe manner using Effect's Stream.
Process Items Concurrently	🟡 Intermediate	Perform an asynchronous action for each item in a stream with controlled parallelism to dramatically improve performance.
Process Items in Batches	🟡 Intermediate	Group items into chunks for efficient bulk operations, like database inserts or batch API calls.
Turn a Paginated API into a Single Stream	🟡 Intermediate	Convert a paginated API into a continuous, easy-to-use stream, abstracting away the complexity of fetching page by page.
Fan Out to Multiple Consumers	🟠 Advanced	Distribute stream data to multiple parallel consumers for processing.
Implement Backpressure in Pipelines	🟠 Advanced	Control data flow rates to prevent overwhelming slow consumers.
Implement Dead Letter Queues	🟠 Advanced	Route failed items to a separate queue for later analysis and reprocessing.
Manage Resources Safely in a Pipeline	🟠 Advanced	Ensure resources like file handles or connections are safely acquired at the start of a pipeline and always released at the end, even on failure.

Making HTTP Requests

HTTP client patterns with Effect

Pattern	Skill Level	Summary
Parse JSON Responses Safely	🟢 Beginner	Use Effect Schema to validate and parse HTTP JSON responses with type safety.
Your First HTTP Request	🟢 Beginner	Learn how to make HTTP requests using Effect's HttpClient with proper error handling.
Add Timeouts to HTTP Requests	🟡 Intermediate	Set timeouts on HTTP requests to prevent hanging operations.
Cache HTTP Responses	🟡 Intermediate	Implement response caching to reduce API calls and improve performance.
Create a Testable HTTP Client Service	🟡 Intermediate	Define an HttpClient service with separate 'Live' and 'Test' layers to enable robust, testable interactions with external APIs.
Handle Rate Limiting Responses	🟡 Intermediate	Gracefully handle 429 responses and respect API rate limits.
Log HTTP Requests and Responses	🟡 Intermediate	Add request/response logging for debugging and observability.
Model Dependencies as Services	🟡 Intermediate	Abstract external dependencies and capabilities into swappable, testable services using Effect's dependency injection system.
Retry HTTP Requests with Backoff	🟡 Intermediate	Implement robust retry logic for HTTP requests with exponential backoff.
Build a Basic HTTP Server	🟠 Advanced	Combine Layer, Runtime, and Effect to create a simple, robust HTTP server using Node.js's built-in http module.

Testing

Test Effect applications

Pattern	Skill Level	Summary
Test Effects with Services	🟢 Beginner	Learn how to test Effect programs that depend on services by providing test implementations.
Your First Effect Test	🟢 Beginner	Write your first test for an Effect program using Vitest and Effect's testing utilities.
Accessing the Current Time with Clock	🟡 Intermediate	Use the Clock service to access the current time in a testable, deterministic way, avoiding direct calls to Date.now().
Mocking Dependencies in Tests	🟡 Intermediate	Use a test-specific Layer to provide mock implementations of services your code depends on, enabling isolated and deterministic unit tests.
Use the Auto-Generated .Default Layer in Tests	🟡 Intermediate	When testing, always use the MyService.Default layer that is automatically generated by the Effect.Service class for dependency injection.
Write Tests That Adapt to Application Code	🟡 Intermediate	A cardinal rule of testing: Tests must adapt to the application's interface, not the other way around. Never modify application code solely to make a test pass.
Organize Layers into Composable Modules	🟠 Advanced	Structure a large application by grouping related services into 'module' layers, which are then composed together with a shared base layer.
Property-Based Testing with Effect	🟠 Advanced	Use fast-check with Effect for property-based testing of pure functions and effects.
Test Concurrent Code	🟠 Advanced	Test race conditions, parallelism, and concurrent behavior in Effect programs.
Test Streaming Effects	🟠 Advanced	Write tests for Stream operations, transformations, and error handling.

Observability

Logging, tracing, and metrics

Pattern	Skill Level	Summary
Debug Effect Programs	🟢 Beginner	Learn techniques for debugging Effect programs using logging, tap, and cause inspection.
Your First Logs	🟢 Beginner	Learn the basics of logging in Effect using the built-in structured logging system.
Add Custom Metrics to Your Application	🟡 Intermediate	Use Effect's Metric module to instrument your code with counters, gauges, and histograms to track key business and performance indicators.
Add Custom Metrics to Your Application	🟡 Intermediate	Use Effect's Metric module to instrument your code with counters, gauges, and histograms to track key business and performance indicators.
Instrument and Observe Function Calls with Effect.fn	🟡 Intermediate	Use Effect.fn to wrap, instrument, and observe function calls, enabling composable logging, metrics, and tracing at function boundaries.
Leverage Effect's Built-in Structured Logging	🟡 Intermediate	Use Effect's built-in logging functions for structured, configurable, and context-aware logging.
Trace Operations Across Services with Spans	🟡 Intermediate	Use Effect.withSpan to create custom tracing spans, providing detailed visibility into the performance and flow of your application's operations.
Trace Operations Across Services with Spans	🟡 Intermediate	Use Effect.withSpan to create custom tracing spans, providing detailed visibility into the performance and flow of your application's operations.
Create Observability Dashboards	🟠 Advanced	Design effective dashboards to visualize your Effect application metrics.
Export Metrics to Prometheus	🟠 Advanced	Expose application metrics in Prometheus format for monitoring and alerting.
Implement Distributed Tracing	🟠 Advanced	Set up end-to-end distributed tracing across services with trace context propagation.
Integrate Effect Tracing with OpenTelemetry	🟠 Advanced	Connect Effect's tracing spans to OpenTelemetry for end-to-end distributed tracing and visualization.
Set Up Alerting	🟠 Advanced	Configure alerts to notify you when your Effect application has problems.

Tooling and Debugging

Debug and profile Effect applications

Pattern	Skill Level	Summary
Read Effect Type Errors	🟢 Beginner	Learn how to read and understand Effect's TypeScript error messages.
Set Up Your Effect Development Environment	🟢 Beginner	Configure your editor and tools for the best Effect development experience.
Configure Linting for Effect	🟡 Intermediate	Set up Biome or ESLint with Effect-specific rules for code quality.
Set Up CI/CD for Effect Projects	🟡 Intermediate	Configure GitHub Actions to build, test, and deploy Effect applications.
Supercharge Your Editor with the Effect LSP	🟡 Intermediate	Install the Effect Language Server (LSP) extension for your editor to get rich, inline type information and enhanced error checking for your Effect code.
Use Effect DevTools	🟡 Intermediate	Debug Effect applications with specialized developer tools.
Profile Effect Applications	🟠 Advanced	Measure and optimize performance of Effect applications.
Teach your AI Agents Effect with the MCP Server	🟠 Advanced	Use the Effect MCP server to provide live, contextual information about your application's structure directly to AI coding agents.