# SysOSX API — access and authentication

The SysOSX API is public. There is no account, no API key and no OAuth:
any client — a browser, a script or an AI agent — may call the endpoints
below directly. This page is the whole authentication story; if a client
asks how to authenticate to SysOSX, the answer is that it does not need
to.

- API documentation: https://www.sysosx.com/api-docs/
- OpenAPI 3.1 specification: https://www.sysosx.com/openapi.json
- Health probe: `GET https://www.sysosx.com/api/check/ping`

## Rate limits

Limits exist to keep shared upstream services and target sites from
being hammered, and they are enforced per visitor IP — there is no
account tier and no way to buy a higher limit.

- Fresh checks share one budget per IP: 20 per hour, with a burst of
  5 per minute.
- Cached results are cheaper and get a separate, larger budget:
  60 per hour per IP. Most repeat checks inside the cache window are
  served from cache and say so (`"cached": true` in the response).
- Some tools have stricter per-tool buckets on top of the shared one:
  bulk domain batches are limited to 3 per hour per IP, and
  agent-readiness scans to 10 per hour per IP.
- When a limit is hit, the API answers `429` with error code
  `RATE_LIMITED` and a `Retry-After` header. Wait for the interval it
  names instead of retrying immediately.

## Identifying your client

No credential identifies a client, so the `User-Agent` header is the
only identity the API sees. Agents and scripts should send a
descriptive one — the product name, what the client is doing, and
ideally a contact or project URL, for example
`MyResearchAgent/1.0 (+https://example.com/about)`. Honest,
descriptive user agents are welcomed; the site's robots.txt policy
deliberately allows the major AI crawlers.

## Where things live

- OpenAPI specification: https://www.sysosx.com/openapi.json
- API documentation (human-readable): https://www.sysosx.com/api-docs/
- Site summary for language models: https://www.sysosx.com/llms.txt
- Full site text, tools, prices and articles: https://www.sysosx.com/llms-full.txt
- Agent-facing catalog: https://www.sysosx.com/.well-known/ai-catalog.json
- Agent card: https://www.sysosx.com/.well-known/agent-card.json
- API catalog (RFC 9727 linkset): https://www.sysosx.com/.well-known/api-catalog

## Contact

Questions about the API, the limits, or a result that looks wrong:
johnlu1976@outlook.com