Postbin Ultra

A native HTTP request inspector for macOS, Linux, and Windows. Capture any method, any path, any payload on a port you choose, and inspect every request the way you actually want to read it — JSON tree view with collapse/expand, syntax-highlighted XML and HTML, forward proxy with one-click replay, attempt history, method-chip filters. Built in Rust + egui, runs entirely on your machine, ships as a single ~10 MB binary.

Full documentation: mpjhorner.github.io/PostbinUltra · Install · Forward + replay · Changelog

Why

Most request bins are SaaS tools. You sign up, get a random URL, copy it into the system you're debugging, wait for traffic to round-trip through someone else's cloud. Postbin Ultra is the local alternative — point your webhook source, SDK, or test harness at http://localhost:9000, every request is captured and rendered immediately. No accounts, no tunnels, no rate limits, no data leaving your machine.

Install

🚀 macOS + Linux — one line

curl -sSL https://raw.githubusercontent.com/MPJHorner/PostbinUltra/main/scripts/install.sh | bash

Detects your OS + arch, grabs the right release artefact, drops PostbinUltra in /Applications (macOS) or ~/.local/bin/ (Linux), tells you how to launch it. That's it.

Other platforms / manual install / build from source are listed on the install page — .dmg for macOS, .tar.gz for Linux, .zip for Windows, cargo install --git … for the Rust toolchain users.

Quick start

1. Launch Postbin Ultra. Top bar shows the capture URL — click the pill to copy.
2. Send anything HTTP to it:

   curl -X POST http://127.0.0.1:9000/webhook \
     -H 'content-type: application/json' \
     -d '{"event":"user.created","id":42}'

3. Click the row in the sidebar. Five tabs across the top: Body (JSON tree, collapsible), Headers, Query, Raw, Forwarded.

Features

• JSON tree view — collapsible objects/arrays + Expand all / Collapse all controls
• Syntax highlighting — JSON, XML, HTML
• Forward + replay — turn Postbin into a transparent proxy. Every captured request stores the upstream response. Click Replay to fire it again — every attempt lands in an attempt-history table.
• Per-request attempt history — replay 50 times to chase an intermittent bug; compare 200 → 500 → 200 across deploys
• Method-chip filter + free-text filter (path, method, headers, body)
• Forward pill in the top bar — shows the upstream host with ↗ accent when on. Shift-click to toggle without leaving the main view.
• Pause / resume / clear capture, Dark / Light / System theme
• Bundled fonts — Inter for UI, JetBrains Mono for code. Identical look on every platform.
• Settings file persists across launches:
  • macOS — ~/Library/Application Support/PostbinUltra/settings.json
  • Linux — $XDG_CONFIG_HOME/postbin-ultra/settings.json
  • Windows — %APPDATA%\PostbinUltra\settings.json

Keyboard shortcuts

Key	Action
j / ↓	Next request
k / ↑	Previous request
g	Jump to most recent
1-4	Body / Headers / Query / Raw tab
p	Pause / resume capture
t	Cycle theme
Shift+X	Clear all captures
,	Open Settings

Sample requests

make sample

Fires 25 realistic-looking requests at http://localhost:9000 — Stripe / GitHub / Slack / SendGrid webhooks, multipart uploads, SOAP XML, GraphQL, raw JPEG PUT, OPTIONS preflight, etc. Useful for trying the UI without setting up a real upstream.

Documentation

The site is the canonical user-facing docs:

• Install — every platform + checksum verification
• Quick start — first request to inspected in 2 minutes
• Forward + replay — proxy mode, attempt history, the Replay button
• Configuration — every Settings tab + field
• Use cases — webhook debugging, SDK inspection, replay-against-staging
• Comparison — vs webhook.site, ngrok inspect, RequestBin, mitmproxy
• Logging — JSON-lines log file format
• Contributing — workspace layout, test policy, release flow
• Changelog — every release

In-repo contributor docs:

• docs/architecture.md — capture pipeline, store events, forward outcome shape
• docs/build-from-source.md — workspace structure, make targets, font + icon regeneration

Contributing

Issues and pull requests welcome. make check before submitting; if you're adding a feature, add a test alongside. Full conventions on the contributing page.

License

MIT © 2026 Matt Horner.