Open Source Desktop App

Test real-time APIs
with confidence

Bytowl is a Postman-like desktop client for WebSocket, STOMP, and Socket.IO endpoints. Connect, send messages, write tests, record sessions, and stream audio — all in one app.

Bytowl main interface showing WebSocket connection with live message stream

Three protocols.
One app.

No more switching between tools. Bytowl speaks all major real-time protocols natively.

WS

WebSocket

Connect to any WebSocket endpoint. Send text or binary messages. Watch live responses stream in.

STOMP

STOMP

Full STOMP 1.2 support with topic subscriptions, destination routing, and heartbeat configuration.

IO

Socket.IO

Connect to Socket.IO namespaces, emit custom events, and listen for server-pushed messages.

Everything you need to
debug real-time APIs

Automated Testing

Write tests that run on every message

Write JavaScript or Python test scripts that execute automatically on each incoming message. Assert on response properties, validate schemas, and export test reports as HTML or PDF.

  • JavaScript & Python support
  • Syntax highlighting & error checking
  • Code snippets library
  • Export reports as HTML/PDF
Tests tab showing JavaScript test code with passing test results
Audio Streaming

Stream microphone audio to endpoints

Capture microphone input and stream audio chunks directly to your WebSocket or Socket.IO endpoint. Perfect for testing speech-to-text services, audio processing pipelines, and real-time voice apps.

  • PCM 16-bit, 32-bit float, WAV, Opus
  • Configurable sample rate & chunk size
  • Live waveform visualization
  • Base64 or binary transport
Audio tab showing microphone streaming with waveform and chunk log
Record & Replay

Capture sessions, replay them later

Record every send, receive, and subscribe action in a session. Replay recordings against live endpoints with diff mode to catch regressions, or test mode to validate behavior.

  • Step-by-step recording
  • Diff mode compares expected vs actual
  • Editable recorded steps
  • Audio chunk replay support
Recorder tab showing captured session steps
Replay with Diff

Spot regressions instantly

Replay a recorded session and see exactly what changed. Diff mode highlights mismatches between the baseline recording and the current response, making regression testing effortless.

  • Side-by-side diff view
  • Pass/fail status per step
  • Live progress indicator
  • Test mode for CI-style assertions
Replay modal with diff mode showing pass and fail results

And there's more

Environment Variables

Define variables per environment and reference them in URLs, headers, and message bodies with {{variable}} syntax.

Workspaces & Folders

Organize connections into workspaces and folders. Drag-and-drop to reorder. Export and import entire folders as JSON.

Syntax Highlighting

JSON, XML, JavaScript, and Python highlighting in message editors and test scripts, with variable overlays.

Git Integration

Connect a Git repository to version-control your workspace. Push and pull collections and environments via the built-in Git sync.

AsyncAPI Import

Import AsyncAPI specs to auto-generate connection collections with the right protocols, endpoints, and topics pre-filled.

Multi-Tab Interface

Open multiple connections as tabs and switch between them instantly. Each tab keeps its own state, messages, and test results.

Ready to test
your real-time APIs?

Download Bytowl for free and start debugging WebSocket, STOMP, and Socket.IO endpoints in minutes.

Download for macOS
v1.0.0 · macOS 12+ · Free & Open Source

Windows and Linux builds coming soon.