Best Free API Development Tools

Proxy your API, choose which endpoints to mock in the cloud and inspect traffic, for free. Speed up your development and integration tests. The page we cite for this offer states no amount, tier or rate we can read when we last looked, on 2026-10-10, so we cannot confirm these terms today.

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-10-10, could read no amount, tier or rate on the page. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

API marketplace and hub — free to sign up and browse. Individual APIs set own free tiers (typically 500-1K req/mo). Platform rate limits: 1,000 req/hr, 500K req/mo. No platform fee on free API tiers. We could not read the page we cite for this offer when we last looked, on 2026-11-13, so we cannot confirm these terms today.

• −1 stale_verification We cannot confirm this offer: 9 consecutive re-check attempts have failed (most recently 2026-11-13 — page content too short (likely JS-rendered SPA); the rendering client failed: the rendering client did not finish in time), never confirmed since it was indexed. This is our inability to verify, not a change by the vendor. (a limit of ours, not a change by the vendor)

Post HTTP Requests Online. Popular Request Methods include GET, POST, PUT, DELETE, and HEAD. Supports Headers and Token Authentication. Includes a basic login system for saving your requests. The page we cite for this offer states no amount, tier or rate we can read when we last looked, on 2026-10-29, so we cannot confirm these terms today.

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-10-29, could read no amount, tier or rate on the page. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

API design, debugging, testing, and documentation platform — free tier: up to 4 users, unlimited projects, unlimited APIs, unlimited requests. API mocking included. 7-day change history

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-10-29, found the page different from the terms we hold. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

Treblle helps teams build, ship, and govern APIs. With advanced API log aggregation, observability, docs, and debugging. You get all features for free, but there is a limit of up to 250k requests per month on the free tier. The page we cite for this offer states no amount, tier or rate we can read when we last looked, on 2026-10-10, so we cannot confirm these terms today.

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-10-10, could read no amount, tier or rate on the page. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

Automatically generate RESTful API documentation with Swagger 2.0 for Go. Annotate your handler functions, run swag init, and get a Swagger UI endpoint; works with chi, gin, echo, fiber and net/http. Free and MIT-licensed, with optional sponsorship through Open Collective. The page we cite for this offer states no amount, tier or rate we can read when we last looked, on 2026-10-15, so we cannot confirm these terms today.

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-10-15, could read no amount, tier or rate on the page. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

Free OSS (MIT). API development ecosystem — REST, GraphQL, WebSocket, SSE, Socket.IO, MQTT testing. Real-time collaboration, environments, collections. Web, desktop, and CLI. The page we cite for this offer states no amount, tier or rate we can read when we last looked, on 2026-10-25, so we cannot confirm these terms today.

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-10-25, could read no amount, tier or rate on the page. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

Proxy service for inspecting and debugging API calls. The free plan includes 10,000 requests per month. We could not read the page we cite for this offer when we last looked, on 2026-11-13, so we cannot confirm these terms today.

• −1 stale_verification We cannot confirm this offer: 9 consecutive re-check attempts have failed (most recently 2026-11-13 — page content too short (likely JS-rendered SPA); a rendering client read 476 characters), never confirmed since it was indexed. This is our inability to verify, not a change by the vendor. (a limit of ours, not a change by the vendor)

The Amazon Selling Partner API (SP-API) is for building seller and vendor tools on Amazon. SP-API is free for sellers and third-party developers. Amazon announced a $1,400 annual fee for developers and per-call fees in late 2025, but delayed and then postponed them. In May 2026, Amazon said it "will not move forward with the SP-API usage and annual fees at this time.". The page we cite for this offer does not name it when we last looked, on 2026-10-10, so we cannot confirm these terms today.

• −1 stale_verification We cannot confirm this offer: 1 consecutive re-check attempt has failed (most recently 2026-10-10 — the page never names Amazon SP-API and is not served from its domain), never confirmed since it was indexed. This is our inability to verify, not a change by the vendor. (a limit of ours, not a change by the vendor)

Get instant access to over 120+ APIs for free, built with quality, consistency, and reliability in mind. The free plan covers up to 50 API Tokens per month. (Possibly taken down, 2025-06-25). When we last read the page we cite for this offer, on 2026-11-10, we found a change we could not reconcile with the terms we publish, so we cannot confirm these terms today.

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-11-10, found the page different from the terms we hold. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

Visually create Open API 3 definitions for free. The page we cite for this offer states no amount, tier or rate we can read when we last looked, on 2026-10-10, so we cannot confirm these terms today.

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-10-10, could read no amount, tier or rate on the page. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

Suite of 15 REST APIs (IP geolocation, email validation, screenshots, exchange rates, phone validation, etc.) — free tier: 1,000 requests/month per API, 1 request/second rate limit. Non-commercial use only on free tier. When we last read the page we cite for this offer, on 2026-11-01, we found the same terms as an earlier read we had declined to record, so we cannot confirm these terms today.

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-11-01, found the same terms as an earlier read we had declined to record. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

Free public mock REST APIs: 200+ endpoints across 9 domains (e-commerce, finance, recruitment, education, healthcare, socials, markets, meteorology and aviation) with full CRUD, filtering and pagination. No signup and no API keys. Custom mock APIs are the paid Developer plan: $10/month after a 7-day free trial, with 50,000 API calls a month and 20 projects. The page we cite for this offer states no amount, tier or rate we can read when we last looked, on 2026-10-22, so we cannot confirm these terms today.

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-10-22, could read no amount, tier or rate on the page. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

API design and documentation platform — free tier: 1 user, 1 project. Includes OpenAPI visual designer, API editor, interactive docs, API console, code generation, Git sync, automatic SSL

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-11-12, found the page different from the terms we hold. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

Create a fake REST API from a JSON object, and customize HTTP status codes, headers, and response bodies. The page we cite for this offer states no amount, tier or rate we can read when we last looked, on 2026-10-10, so we cannot confirm these terms today.

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-10-10, could read no amount, tier or rate on the page. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

Create a free endpoint to which you can send HTTP requests. Any HTTP requests sent to that endpoint will be recorded with the associated payload and headers so you can observe recommendations from webhooks and other services. The page we cite for this offer does not name it when we last looked, on 2026-10-22, so we cannot confirm these terms today.

• −1 stale_verification We cannot confirm this offer: 1 consecutive re-check attempt has failed (most recently 2026-10-22 — the page never names RequestBin.com, on a domain that carries its name), never confirmed since it was indexed. This is our inability to verify, not a change by the vendor. (a limit of ours, not a change by the vendor)

Quickly auto-generate models/class/type/interface and serializers from JSON, schema, and GraphQL for working with data quickly & safely in any programming language. Convert JSON into gorgeous, typesafe code in any language. The page we cite for this offer states no amount, tier or rate we can read when we last looked, on 2026-10-14, so we cannot confirm these terms today.

• −1 stale_verification Our last read of the vendor's pricing page, on 2026-10-14, could read no amount, tier or rate on the page. This is our confidence in the record, not a change by the vendor. (a limit of ours, not a change by the vendor)

API design and documentation platform (SmartBear) — no permanent free tier. Swagger's own pricing FAQ, read 2026-09-05: "You can get started with Swagger with a free trial, no credit card required, then choose the plan that best fits your usage and requirements." The same FAQ puts the free Swagger tools on the open-source side — Swagger Editor, Swagger UI and Swagger Codegen, run locally — and SwaggerHub among the commercial products. Plan prices are client-rendered and were not read. Note — discovered 2026-04-13: Free community plan replaced by trial only Source ↗

• −3 free_tier_withdrawn Recorded free tier removal on 2026-04-13: Free community plan replaced by trial only Source: https://swagger.io/product/pricing/
• −2 time_limited_offer Tier "Trial" is a trial that expires, not an ongoing free tier.
• −1 stale_verification We cannot confirm this offer: 1 consecutive re-check attempt has failed (most recently 2026-11-06 — The pricing page text is truncated and contains only FAQ headings and navigation links; it does not state whether a free trial still exists, what its limits are, or any plan pricing, so the stored trial-tier info cannot be verified.), never confirmed since it was indexed. This is our inability to verify, not a change by the vendor. (a limit of ours, not a change by the vendor)