Open-Source Observability · open-source-labs

Swell

Swell is a desktop API testing tool built for developers who work with modern streaming protocols like WebSockets, Server-Sent Events, HTTP/2, GraphQL, gRPC, and tRPC. It provides a Postman-like interface for composing, sending, and monitoring requests across these technologies, plus features like stress testing, workspace management, and JavaScript-based test scripting.

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Source: GitHub — github.com/open-source-labs/Swell

983

GitHub stars

144

Forks

JavaScript

Primary language

MIT

License (OSI-approved)

Key facts

Objective fields from the source. Values we can't verify are shown as “Unknown” rather than guessed.

Field	Value
Repository	open-source-labs/Swell
Owner	open-source-labs
Primary language	JavaScript
License	MIT — OSI-approved
Stars	983
Forks	144
Open issues	9
Latest release	v1.19.0 (2025-02-14)
Last updated	2025-02-14
Source	https://github.com/open-source-labs/Swell

What Swell is

Swell is an Electron-based (JavaScript/Node.js) application that handles HTTP/2 multiplexing, WebSocket connections, SSE event streams, GraphQL introspection and subscriptions, gRPC unary/streaming, tRPC batch operations, and WebRTC SDP negotiation. It supports local workspace persistence, custom mock servers, and Chai-style assertion testing within a single desktop client.

Quickstart

Get the Swell source

Clone the repository and explore it locally.

terminalbash

1git clone https://github.com/open-source-labs/Swell.git2cd Swell3# follow the project's README for install & configuration

Need it deployed, integrated, or customized instead? DEV.co ships production installs.

Best use cases

GraphQL API Development & Testing

Full support for queries, mutations, subscriptions, and introspection makes Swell ideal for teams building and iterating on GraphQL backends during development cycles.

Real-time & Streaming Protocol Testing

Developers working with WebSockets, SSE, gRPC, or tRPC can test bidirectional communication and stream handling without writing custom client code.

Stress Testing Modern APIs

Built-in stress testing for HTTP/2 and GraphQL endpoints helps validate backend performance under concurrent load before production deployment.

Implementation considerations

Swell runs as a desktop application on OSX, Linux, and Windows; requires individual installation per developer workstation.
Workspace and test data persist locally; plan for manual export/import or version control of .json workspace files if team sharing is needed.
Test suites use Chai-style assertions in JavaScript; developers should be comfortable with TDD/BDD syntax and JavaScript syntax.
Mock server feature is marked experimental; evaluate stability and feature completeness before relying on it for production-grade mocking.
No built-in authentication or secrets management; sensitive API keys and credentials must be managed externally or stored securely outside the tool.

When to avoid it — and what to weigh

Heavy CI/CD Integration Required — Swell is a desktop GUI tool; it is not designed as a headless or command-line testing framework for automated CI/CD pipelines.
Enterprise API Gateway or Centralized Request Logging — Swell lacks built-in API gateway, request centralization, or audit logging features needed for large-scale enterprise API management and compliance.
Cross-platform Team Collaboration in Real-time — Workspaces are stored locally; there is no native cloud sync, role-based access control, or real-time collaboration features for distributed teams.
Legacy or Proprietary Protocol Support — Swell focuses on modern streaming and RPC protocols; custom or legacy protocols not listed (SSE, WS, HTTP/2, GraphQL, gRPC, tRPC, WebRTC) would require workarounds or are unsupported.

License & commercial use

Swell is licensed under the MIT License, a permissive OSI-approved license allowing modification, distribution, and commercial use with minimal restrictions, provided the license notice is retained.

MIT License permits commercial use of the software. However, review the LICENSE.txt file and consult legal counsel if bundling Swell into a proprietary product or service, or if building a derivative commercial product, to ensure compliance with attribution and notice requirements.

DEV.co evaluation signals

Editorial assessment — not user reviews. Directional, with an explicit confidence level.

Signal	Assessment
Maintenance	Active
Documentation	Adequate
License clarity	Clear
Deployment complexity	Low
DEV.co fit	Good
Assessment confidence	High

Security considerations

Swell is a local desktop tool with no built-in encryption for stored workspaces; ensure workspaces containing API keys or sensitive payloads are stored on encrypted filesystems. The tool sends requests to external endpoints—validate TLS/SSL certificate handling for HTTPS connections and confirm that request headers/bodies are not logged or telemetrized without user consent. No security audit data is available in the provided information; if handling sensitive data, independent review is advised.

Alternatives to consider

Postman

Mature, widely-adopted API testing platform with cloud collaboration, CI/CD integrations, mock servers, and extensive protocol support; better for enterprise teams but lacks specialized streaming protocol features like gRPC and tRPC out-of-the-box.

Insomnia

Desktop-based REST and GraphQL client with workspace sync, plugin ecosystem, and authentication support; lighter-weight than Postman but offers fewer streaming protocol options and less stress-testing capability than Swell.

gRPC GUI Clients (e.g., BloomRPC, Evans)

Specialized tools for gRPC testing; if gRPC is the primary use case, these tools may be more focused and lightweight, though they lack Swell's multi-protocol breadth and scripting features.

Software development agency

Build on Swell with DEV.co software developers

Download Swell for free and start testing WebSockets, GraphQL, gRPC, and more. Perfect for developers building real-time and streaming applications.

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Swell FAQ

Can Swell be integrated into my CI/CD pipeline?

Swell is a desktop GUI and not designed as a headless testing framework. To integrate with CI/CD, you would need to export workspaces and parse results manually or write custom scripts to invoke the CLI (if available—not clearly documented). Consider alternatives like Postman CLI or custom test harnesses for pipeline integration.

Does Swell support team collaboration and cloud sync?

No. Workspaces are stored locally on each developer's machine. Sharing requires manual JSON export/import. For team collaboration, consider Postman or Insomnia, which offer cloud sync and team workspaces.

What platforms are supported?

Swell runs on OSX, Linux, and Windows as a standalone desktop application.

Is Swell suitable for production monitoring?

No. Swell is a development and testing tool, not a production monitoring or observability platform. Use APM tools (e.g., Datadog, New Relic) for production API monitoring.

Software developers & web developers for hire

Adopting Swell is usually one piece of a larger software development effort. As a software development agency, DEV.co provides software development services and web development expertise — pairing senior software developers and web developers with your team to design, build, and operate open-source observability software in production.

Ready to Test Modern APIs?

Download Swell for free and start testing WebSockets, GraphQL, gRPC, and more. Perfect for developers building real-time and streaming applications.

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