20 Best Open Source API Clients & Postman Alternatives for 2025

6 min read3 days ago

Postman may have set the standard for API clients, but the world of API tooling has exploded with innovative, open-source, and privacy-first alternatives. Whether you’re a developer seeking a lightweight desktop app, a CLI enthusiast, or a team looking for secure, collaborative API management, there’s a perfect tool for you. Here’s a fresh look at 20 outstanding API clients and utilities that are redefining the API landscape in 2025.

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1. Apidog

Apidog is a unified platform for API design, testing, mocking, and documentation. Its intuitive interface, strong free plan, and enterprise-grade features make it a top pick for teams managing the full API lifecycle.

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Why Apidog?

Combines Postman, Swagger, and mock server features in one app
Team-based workflows with granular access controls
Ideal for fintech, SaaS, and enterprise use
Available on desktop and web

2. Firecamp

Firecamp is a browser-based workspace for collaborative API development. It’s designed for real-time API testing and supports a wide range of protocols.

REST, GraphQL, WebSocket, and gRPC support
Visual and code-based client views
VS Code-inspired interface
Built-in team collaboration

3. Prestige

Prestige is a browser-based API client for those who love Markdown-style, plain-text HTTP requests.

Compose/send requests with minimal syntax
Fully offline and open-source
Syntax highlighting and expandable panels

4. gRPC UI

gRPC UI brings a visual interface to gRPC endpoints, making it easy to explore and test services without writing code.

Auto-loads .proto files
Real-time gRPC method testing
Great for microservices and backend teams

5. Restfox

Restfox is a privacy-first, browser-based HTTP client with an offline-first design and a minimal, fast interface.

Works offline, no cloud required
Tabbed layout, request history
Lightweight and resource-efficient

6. Yaade (Web Edition)

Yaade is a self-hosted, open-source API client for privacy-focused teams.

Encrypted, persistent storage
Multi-user authentication
Perfect for on-premise and secure environments

7. Requestly

Requestly is a browser extension and web tool for intercepting, mocking, and debugging API calls directly in your browser.

API mocking, redirection, and modification
Browser extension and web client
Custom rules for streamlined debugging

8. Hoppscotch

Hoppscotch is a fast, browser-based API client supporting REST, GraphQL, WebSocket, and more.

No install needed — just open in your browser
REST, GraphQL, WebSocket, SSE, MQTT
Workspaces, collections, and environment variables
Open-source and actively developed

9. Bruno

Bruno is a file-based, open-source API client for offline use, with YAML/JSON request management and Git compatibility.

File-based config, perfect for version control
REST, GraphQL, and (soon) gRPC
Scriptable with JavaScript

10. Yaak

Yaak is a native desktop API client with a clean, tab-based interface for quick REST API testing.

REST support, tabbed navigation
Minimal setup, user-friendly

11. API Dash

API Dash is a cross-platform, open-source API client with a modern UI and support for request history and collections.

REST testing, tabs, environment variables
Windows, macOS, Linux support

12. ezy

ezy is a graphical gRPC/gRPC-Web client with a focus on protocol-specific testing and Protobuf management.

gRPC/gRPC-Web calls
GUI for Protobuf

13. BloomRPC

BloomRPC is a legacy GUI for gRPC services — still useful for older workflows.

Proto file management
Real-time request/response

14. Milkman

Milkman is a plugin-friendly API workbench supporting REST, GraphQL, SOAP, and more.

Plugin architecture for protocol support
Workspace-based, export/import environments

15. Insomnium

Insomnium is a privacy-first fork of Insomnia, storing everything locally for offline and secure use.

100% local storage, no cloud
Full Insomnia feature set

16. Cartero

Cartero is a native, minimalist HTTP client for quick, repeated API testing.

Multi-platform, direct HTTP inspection

17. Nightingale REST Client

Nightingale is a Windows-native REST client with a modern, resource-light interface.

Tabbed UI, environment management
Mock server deployment

18. VS Code REST Client

A must-have VS Code extension for sending HTTP requests directly from .http or .rest files.

Inline requests and responses
Syntax highlighting, environment support

19. Pororoca

Pororoca is a network debugging tool with strong HTTP/2 and HTTP/3 support for modern web protocol inspection.

Inspect HTTP/1.1, HTTP/2, HTTP/3
Deep packet inspection, fast and lightweight

20. ATAC

ATAC is a terminal-based API client with a menu-driven TUI for fast, structured HTTP requests.

TUI with form-based inputs
History and request management
Cross-platform (Linux, macOS, Windows/WSL)

Bonus: CLI Tools & Automated Testing

curl: The classic terminal HTTP tool
HTTPie: Human-friendly CLI for HTTP requests
grpcurl: gRPC for the terminal
xh, curlie: Fast, modern HTTP CLIs
HttpRepl, posting, ain, evans, httpYac, ATAC: Specialized CLI utilities

Automated Testing & Load Testing:

Hurl, Karate, Tavern, Venom, pyresttest: For CI/CD and scenario testing
runn, scenarigo, Schemathesis, Dredd, abao, HttpRunner: Contract and OpenAPI validation
k6, Artillery: High-performance load testing

Conclusion: The API Client Ecosystem Has Never Been Richer

In 2025, developers are spoiled for choice. From browser-based tools like Hoppscotch to CLI powerhouses like HTTPie, and all-in-one platforms like Apidog, there’s an API client for every workflow. Explore, experiment, and build your perfect toolkit — your productivity (and your APIs) will thank you!