Errors and limits

Problem Details errors with stable codes, the per-IP rate limit, and the headers that come with them.

Errors

Errors use Problem Details (RFC 9457) with Content-Type: application/problem+json. The type URL ends in a stable code, which is repeated in code.

{
  "type": "https://arxivv.org/errors/not-found",
  "title": "Not found",
  "status": 404,
  "detail": "Unknown paper 1706.99999",
  "instance": "/1706.99999.md",
  "code": "not-found"
}

• Match on code (or the code in type), not on title or detail. Codes are stable within a schema major.
• Error responses carry X-Arxivv-Schema, Vary: Prefer and Cache-Control: no-store.
• Drop-in routes return arXiv’s own error responses unchanged. Only an unreachable arXiv becomes 502 upstream.

Rate limit

When you exceed it:

HTTP/2 429
Content-Type: application/problem+json
Retry-After: 60
Cache-Control: no-store

{
  "type": "https://arxivv.org/errors/rate-limited",
  "title": "Rate limit exceeded",
  "status": 429,
  "detail": "Too many requests; retry in a minute",
  "instance": "/1706.03762.md",
  "code": "rate-limited"
}

• No sign-up or API key is needed.
• The limit is counted per Cloudflare location and is approximate.
• Responses served from Cloudflare’s cache never reach the Worker, so they do not count.
• Requests to https://arxivv.org/mcp count like any other request.
• Need more? Get in touch; limits are configuration, not code.

Headers