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Aug 3, 2021

License: MIT Build Status GitHub package.json version contributions welcome Tweet

Swell is a API development tool that enables developers to test endpoints served over streaming technologies including Server-Sent Events (SSE), WebSockets, HTTP2, GraphQL and gRPC.

Getting Started

Visit to download the latest release.

Swell is currently available for OS X, Linux and Windows.


Swell is a one-stop shop for sending and monitoring your API requests

  • Send and monitor streams over HTTP2 / HTTP1 (including SSEs) and WebSockets
  • Create GraphQL queries, introspections, mutations, and subscriptions
  • Make API requests based on a range of provided options that conform to the specifications defined in an OpenAPI document.
  • Verify STUN and TURN server connectivity for WebRTC applications by generating an SDP
  • Provides full streaming testing support for gRPC
  • View response timing information and history in an interactive chart for each request
  • Save workspaces of multiple requests for later access
  • Import and export workspaces for sharing
  • Compose test suites in JavaScript with Chai-style TDD/BDD assertion syntax
  • Execute a collection of requests in succession and receive clear visual feedback of each test's status
  • Schedule requests on to be sent on a regular time interval to support endpoint functional validation tests

Supported Technologies

  • HTTP2: Swell supports full HTTP2 multiplexing of requests and responses. HTTP requests to the same host will be sent over the same connection. Swell will attempt to initiate an HTTP2 connection for all HTTPS requests by default, but will revert to HTTP1.1 for legacy servers. Multiple concurrent streams are allowed for each connection.

  • Server-Sent Events (SSE): Initiated by a simple toggle box, Swell displays SSE events one by one as they come in. Similar to HTTP2 streams, multiple open connection streams are allowed for SSE.

  • WebSocket (WS): Swell enables connecting directly to WebSocket servers with an HTTP handshake. Developers can directly send messages to the connected WS server. Messages are displayed in chatbox format, clearly indicating outgoing and incoming messages.

  • GraphQL: Swell includes full support for all three root types of GraphQL - queries, mutations, and subscriptions as well as Introspection - with and without variables. Smart code editor allows for easy query creation.

  • gRPC: Swell includes full support for all four streaming types of gRPC - unary, client stream, server stream, bidirectional stream.

  • OpenAPI: Swell supports the enumeration and execution of REST and RPC API requests as defined in a user-provided OpenAPI document.

  • WebRTC: Swell enables testing STUN and TURN ICE server connectivity for WebRTC applications.

    Developers enter ICE server details as an array of JavaScript objects (example code block below). An RTCPeerConnection is instantiated and an SDP is generated.

        urls: 'turn:111.222.333.444:54321',
        username: 'myAwesomeUsername',
        credential: 'mySecretPassword',  // or token
        credentialType: 'password'
        urls: 'stun:555.777.888.999:43210',

Additional Features

  • Scripting in Swell: Swell allows you to write assertion tests to aid in the test-driven development cycle of backend API services.
  • Workspaces: Swell allows you to save workspaces for easier testing of multiple requests.
  • Import/Export Workspaces: Swell allows you to import and export workspaces, making it easy to share collections with your team.
  • Preview: You can now view a rendered preview of certain API responses (HTML)
  • Collection Runner: You can also stage requests in the workspace and automate the process of sending off each one. No need to manually press send on each one, instead each request will fire off in the order of staging.
  • Schedule Tests: You can also automate sending requests to occur on a periodic basis.

Built With

  • Electron
  • React
  • Redux
  • Apollo Client
  • Websockets
  • gRPC-js
  • VM2
  • Chart.js
  • Bulma
  • IndexedDB
  • Chai
  • Mocha



This project is licensed under the MIT License