API Development & Testing

CH

Checkly

4.6/5.01 verified review

Freemium

Code-first synthetic monitoring and continuous testing platform built for modern engineering teams.

• Full code-first monitoring definition using TypeScript and Playwright.
• Distributed test execution across multiple global regions.
• Deep integration with CI/CD pipelines and developer tools.

FU

FusionAuth

4.6/5.01 verified review

Freemium

API-driven CIAM platform with flexible deployment and total control

• Fully API-driven architecture for custom automation and workflows
• Self-hosted Docker container deployment for air-gapped environments
• Native support for modern authentication standards including passkeys

LL

Levanto Labs

4.5/5.01 verified review

Freemium

Decision model API for extracting structured data and streaming decisions in real time.

• Precise extraction of typed fields from natural language via API.
• Streaming decisions optimized for low latency in production.
• Support for image input and conditional reasoning.

CA

Castov

4.5/5.01 verified review

Free·Open Source·MIT

Fast, 100% client-side developer platform with CLI and MCP server support.

• 100% local browser and CLI execution with zero telemetry.
• Includes a native Model Context Protocol (MCP) server for Cursor and Claude.
• Over 60 interactive developer tools and chainable data pipelines.

1stars on GitHub

HA

Hasura

4.5/5.01 verified review

Freemium

GraphQL engine and data delivery network for secure APIs and artificial intelligence applications.

• Instant generation of GraphQL APIs from existing relational database schemas
• Role-based access control integrated directly into the data layer
• Support for complex queries, filtering, and pagination without writing repetitive backend code

PI

Pipedream

4.5/5.01 verified review

Freemium

Integration and managed auth layer with 10,000+ tools for AI agents and developers.

• Managed authentication built-in for 3,000+ APIs and third-party services.
• Native Model Context Protocol (MCP) support facilitating AI agent integration.
• SDKs and HTTP proxies to invoke any API directly from code.

10stars on GitHub

DI

DigDeep

4.4/5.01 verified review

Free

Client-side DNSSEC, mail, HTTPS, and DoH analyzer with native browser WebCrypto.

• 100% client-side validation using browser SubtleCrypto without intermediary backend servers.
• Simultaneous comparison across multiple public DoH resolvers with RFC 8914 support.
• Interactive chain-of-trust graph generation with SVG and PNG export capabilities.

MA

MachineMail

4.4/5.01 verified review

Freemium·Open Source·MIT

Email API designed for AI agents and automated workflows.

• Free and dedicated mailboxes for autonomous agents.
• Built-in trust reports on incoming messages for security.
• Full compatibility with the MCP protocol and AgentMail API.

SP

Speechmatics

4.4/5.01 verified review

Freemium·Open Source·MIT

Voice AI APIs for enterprise-grade speech-to-text and transcription in 55+ languages.

• High accuracy with diverse accents.
• Flexible deployment options.
• Comprehensive enterprise compliance.

164stars on GitHub

IN

Insomnia

4.4/5.01 verified review

Freemium·Open Source·Apache-2.0

Collaborative API development and testing platform for HTTP, REST, GraphQL, and gRPC architectures.

• Native support for multiple protocols including REST, GraphQL, gRPC, and WebSockets
• Scratch Pad mode available without requiring user registration or login
• Tight Git version control integration for collection synchronization

40.1kstars on GitHub

SW

Swagger

4.4/5.01 verified review

Freemium

API design, documentation and testing tools built for OpenAPI standards

• Native standardization based on OpenAPI and AsyncAPI specifications
• Automated generation of interactive developer documentation
• Complete ecosystem featuring widely adopted open source components

RE

ReadMe

4.4/5.01 verified review

Paid·Open Source·MIT

Interactive technical documentation platform for APIs and developer tools.

• Automatic generation of API references from OpenAPI specs.
• Documentation components optimized for AI agent readability.
• Built-in version control and branch management features.

147stars on GitHub