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API Design, Development and Testing Tools

A directory of tools across the API lifecycle — designing and documenting, mocking and exploring, load-testing and monitoring, and gateways that publish APIs.

21 topics•5 categories•Updated October 2026

Design, Documentation & Clients

6 entries

Design APIs to a spec and call them by hand.

01Swagger Explore (formerly Swagger Inspector)Test API endpoints and verify responses with a free, simple client that anyone on the team can master. 02OpenAPI SpecificationThe standard, language-agnostic description format for HTTP APIs. 03PostmanPlatform for designing, testing and documenting APIs. 04BrunoOpen-source, Git-friendly API client. 05InsomniaAPI client and design tool for REST, GraphQL and gRPC. 06StoplightAPI design and documentation platform built around OpenAPI.

Mocking & Test Services

4 entries

Fake endpoints to develop and test against.

07httpbinProvides an array of HTTP API endpoint responses that are useful for testing or debugging front ends that send requests. 08JSONPlaceholderA free online REST API you can use whenever you need fake data — serving roughly 3 billion requests each month. 09Mockbin (by Zuplo)Spin up a fixed-response API endpoint in seconds and inspect every request sent to it — free and open source. 10WireMockAPI mocking and service virtualization tool.

Testing, Load & Monitoring

5 entries

Functional checks, load tests and uptime monitoring for APIs.

11AssertibleAutomated QA tools to test and monitor your web services across deployments and environments. 12BlazeMeterAn API and performance load-testing service by Perforce that provides real-time reporting across 20+ open-source frameworks. 13Loader.ioA free load-testing service that lets you stress test your web apps and APIs with thousands of concurrent connections. 14BlazeMeter API Monitoring (formerly Runscope)24/7 API reliability monitoring that validates contracts, uptime, and latency from cloud or private locations. 15APIContext (formerly APImetrics)Synthetic, end-to-end API monitoring that simulates the full customer journey and provides meaningful metrics for hard-to-monitor APIs.

API Gateways

2 entries

Services that publish and secure APIs.

16Amazon API GatewayCreate, maintain, and secure REST, HTTP, and WebSocket APIs at any scale with a fully managed AWS service. 17IBM API ConnectAn enterprise-grade platform for creating, securing, managing, sharing, monetizing, and analyzing custom APIs on-premises and on the cloud.

Related Pages

4 entries

Related directories on this site.

18API Management PlatformsAPI management and gateways. 19Microservices ArchitectureMicroservices hub. 20Service MeshesService mesh implementations. 21Performance Testing ToolsLoad and performance testing.

Frequently Asked Questions

What are API design tools?

They help you describe an API to a specification such as OpenAPI before or while you build it, generate documentation and keep producers and consumers aligned.

What is API mocking?

A mock returns realistic responses without the real backend, so front-end and client teams can build and test before the service is ready.

How is API monitoring different from API testing?

Testing checks behaviour at a point in time, usually in CI. Monitoring runs checks continuously against production and alerts when an endpoint fails or slows.

Do I need an API gateway?

A gateway adds authentication, rate limiting and routing in front of your APIs. Teams with many services or external consumers usually do; see the API Management Platforms page.

Where do httpbin and JSONPlaceholder fit?

They are free public services that echo requests or return fake data, handy for learning and for testing HTTP clients.

Which links may need a manual click?

Links were rechecked in October 2026 and all outbound links on this page returned 200 to automated checks. For related directories, see API Management Platforms, API Security Software, Service Meshes and Kubernetes Ingress Controllers on this site.