Authentication

A key is optional, not required. Version 1 is read-only and the catalog is public, so a request with no key is served — on the Free tier. Make GET requests directly against https://apis.io/api/v1.

Code
curl "https://apis.io/api/v1/search?q=sms"

This matches APIs.io's open-discovery mission: the catalog is public, and there is no endpoint that mutates it.

Sending a key

A key does two things: it raises your rate limit and daily quota, and it unlocks the tier-gated resources (industries, regions, ratings, Insights depth, the Saved Workspace). Send it as a header:

Code
curl -H "x-api-key: $APIS_IO_KEY" "https://apis.io/api/v1/ratings?limit=10"

A Starter key is free with a GitHub sign-in. Pro and Business are self-serve from your account page.

Requesting a resource above your tier returns 402 Payment Required — not 403, and not 429. It is a payment signal, distinct from being rate limited.

The OpenAPI contract declares this as optional authentication: security: [{}, {ApiKeyAuth: []}] — the empty object says a keyless call is acceptable, the second entry says a key is understood.

CORS

The API is served same-origin with apis.io, and responses are browser-friendly, so you can call it directly from web apps and from the agent surfaces.