Is this URL in the index? — GET /why_not

Request

curl \
  -H "x-api-key: $UNLOB_API_KEY" \
  "https://api.unlob.com/why_not?url=<url>"

Behaviour

Answers one of three things. `present` returns the hit. `removed` names the reason — redundant, superseded, stale, access-starved, lost-replacement, or tombstoned-source — and, where one exists, the passage that superseded it. `unknown` means it was never admitted, or was never seen.

Use it before concluding the web is silent on something: an absent URL and an absent topic are different findings.

Costs 1 credit.

Parameters

Responses

Status	Meaning
200	present, removed (with a reason), or unknown.
401	Missing, unknown or revoked key. A key minted moments ago can answer 401 until it propagates to the serving fleet.
429	Over the per-minute rate (spent in credits), or a hard-capped key without the credits this call costs. `retry-after` is present on the rate-limit case only.

The same call over MCP

This capability is why_not on the MCP server, taking the same parameters and returning the same body. A parity test in the API fails the build if the two ever diverge, so you can read either reference and use the other.

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "why_not",
    "arguments": {
      "url": "<url>"
    }
  }
}

Most clients build that frame for you — see Connect a client.

See Errors for what to do with each status, and Retries and backoff for which are worth repeating.

FAQ

What does 200 mean on GET /why_not?

present, removed (with a reason), or unknown.

What does 401 mean on GET /why_not?

Missing, unknown or revoked key. A key minted moments ago can answer 401 until it propagates to the serving fleet.

What does 429 mean on GET /why_not?

Over the per-minute rate (spent in credits), or a hard-capped key without the credits this call costs. `retry-after` is present on the rate-limit case only.