Best API Development & Testing Tools in 2026

ElevenLabs provides the most realistic AI voice technology for content creators and developers. Generate lifelike speech from text in 29 languages. Clone voices with just minutes of audio samples. Real-time voice synthesis for conversational AI applications. API for developers building voice-enabled products. AI voices indistinguishable from human speech.

GoModel is an open-source AI gateway that sits between your applications and AI model providers, offering a unified interface for routing, caching, monitoring, and controlling AI requests. It supports OpenAI and Anthropic SDKs natively, as well as standard chat completions endpoints, making it easy to integrate with existing codebases. The gateway provides a pipeline for authentication, workflow execution, guardrails, caching, rate limiting, and provider routing, with automatic failover and circuit breaker for reliability. Key capabilities include aliases and virtual models for flexible provider routing, scoped workflows for multi-step AI processes, exact and semantic caching to reduce costs and latency, and comprehensive usage analytics and audit logs. Administrators can set budgets, pricing overrides, multiple API keys, and guardrails to enforce safety and cost controls. The dashboard provides visibility into cache performance, prompt cache usage, and request lifecycle. GoModel is available as a free open-source version with core features. A Pro tier adds intelligent routing, context window compression, and OIDC SSO, with cluster mode planned for future release. The roadmap includes plugins, hardened guardrails, streaming image generation, and enhanced dashboard customization.

Apollo Studio provides visibility into your GraphQL APIs. See which queries clients actually run, track performance by field and resolver, and catch schema changes that would break existing clients. The explorer lets developers browse and test queries against your schema interactively. Schema checks in CI prevent breaking changes from reaching production. Contract testing validates that client queries match server capabilities. Teams running GraphQL in production need observability. Apollo Studio provides the monitoring and governance that keep GraphQL APIs healthy as they evolve.

Steampipe is an open-source data-access layer that allows users to query cloud APIs, code, and other data sources using standard SQL. It eliminates the need for complex ETL processes by providing a 'Zero-ETL' approach, treating live cloud configurations and other data as a dynamic database. This enables developers, security professionals, and operations teams to gain real-time insights without syncing or relying on outdated data. The platform leverages a vast library of plugins (over 500) to connect to various services like AWS, Azure, GCP, and many others, organizing their metadata into discoverable SQL tables. This unified SQL interface simplifies tasks such as compliance auditing, security posture assessment, cost optimization, and operational troubleshooting. Steampipe can be used as a CLI tool, or integrated as a PostgreSQL FDW or SQLite extension, making it a versatile tool for anyone needing to analyze and manage their cloud infrastructure and API data efficiently.

Shopify MCP Server is the official Model Context Protocol server from Shopify that gives AI assistants direct access to Shopify's development documentation, GraphQL API schemas, and code validation tools. It enables developers to build Shopify apps faster by letting AI tools like Claude, Cursor, and VS Code provide accurate, up-to-date guidance based on current Shopify APIs. The Dev MCP server searches across all Shopify documentation, explores GraphQL schemas to discover available types, queries, and mutations, and validates generated code against Shopify's APIs. Supported validation covers GraphQL operations, JavaScript/TypeScript component checks, Liquid theme validation for syntax errors and broken references, and individual codeblock testing. It works with the Admin GraphQL API, Storefront API, Customer Account API, Functions, Liquid, Partner API, Payment Apps API, Web Components, POS UI Extensions, and more. Shopify also offers a separate Storefront MCP server for commerce data access (products, carts, customer info) and a Customer Accounts MCP server for order tracking and returns. The Dev MCP server requires Node.js 18+ and is free for all Shopify developers.

Dropbox Sign is an electronic signature platform integrated with Dropbox. Send documents for signature with a simple, intuitive experience. Templates streamline recurring signature workflows. API enables embedding signatures in your applications. Legally binding and compliant with major regulations. E-signatures that feel native to the Dropbox experience.

Stripe is a financial infrastructure platform for internet businesses. Accept payments from anyone, anywhere. Billing handles subscriptions and invoicing. Connect powers marketplace payments. Treasury provides banking as a service. The payments infrastructure that powers millions of businesses from startups to Fortune 500 companies.

Postman is an API development platform used by over 30 million developers and 500,000 organizations worldwide. It provides a unified workspace for designing, testing, documenting, and monitoring APIs across HTTP, GraphQL, gRPC, WebSocket, and MQTT protocols. Teams can collaborate through shared workspaces, collections, and mock servers while maintaining version control via native Git integration. The platform includes an AI-powered agent mode for automating repetitive API tasks, an API catalog for internal service discovery, and a CLI for CI/CD pipeline integration. Postman supports the full API lifecycle from spec design through production monitoring, making it the industry standard for API-first development workflows.

1Password Secrets Automation manages secrets for infrastructure. Programmatic access to 1Password vaults-secrets management for CI/CD and automation. The integration extends 1Password. The automation fits DevOps. The security is inherited. 1Password teams automating secret access use Secrets Automation for programmatic vaults.

MuleSoft Anypoint Platform is an enterprise integration and API management platform owned by Salesforce. It connects applications, data sources, and devices across on-premise and cloud environments through a unified architecture. The platform includes API design, development, and governance tools alongside pre-built connectors for hundreds of systems including Salesforce, SAP, Workday, and AWS. MuleSoft Composer provides low-code integration for business teams, while Robotic Process Automation (RPA) handles legacy system workflows. Intelligent Document Processing (IDP) extracts data from unstructured documents using AI. The platform also supports AI agent development through MuleSoft for Agentforce. Used by enterprises for digital transformation, it is the market leader in integration platforms, though its pricing starts at $57,000/year, making it suitable for mid-market to enterprise organizations.