generated: '2026-08-12'
method: searched
source: >-
  Review of every publicly readable Peer39 API surface — the reference MCP client source
  at https://github.com/awhite07/p39-custom-category-mcp, the connector at
  https://github.com/awhite07/peer39-mcp-connector, and www.peer39.com — plus live probes
  of https://app.peer39.com/api/external/ on 2026-08-12.
api: Peer39 External API

limit_count: 0
headers_published: false
status_on_exhaustion: unknown

detail: >-
  Peer39 publishes no rate limits for the External API, and none can be observed: every
  path under /api/external returns HTTP 401 unauthenticated, so no unauthenticated
  response carries usable headers. The reference client — written against a real, working
  Peer39 account — reads no X-RateLimit-*, RateLimit-* or Retry-After header, implements
  no backoff, and retries only on 401 (re-login), never on 429. That is strong negative
  evidence that the API emits no rate-limit signal an integrator could act on.

limits: []

evidence:
  - url: https://app.peer39.com/api/external/customcategories
    status: 401
    note: unauthenticated GET; no rate-limit headers in the response.
  - url: https://app.peer39.com/api/external/login
    status: 401
    note: POST with empty credentials; no rate-limit headers, no Retry-After.
  - url: https://github.com/awhite07/p39-custom-category-mcp/blob/main/src/api/client.ts
    status: 200
    note: >-
      The complete HTTP layer of Peer39's own reference client. It handles 401 and generic
      !res.ok only — there is no 429 branch and no header inspection.

documented_size_limits:
  note: >-
    Peer39 does publish payload/shape limits, which are not rate limits but are the only
    published quantitative constraints on the API. Recorded here so an integrator finds
    them.
  limits:
    - scope: per-request (list)
      field: max
      limit: 1–999
      note: >-
        Page size. Server-side default is max=0 with start=50, which returns zero rows —
        callers must pass both explicitly. Out-of-range values return error code 50.
    - scope: per-category
      field: items
      limit: 10000
      unit: keywords or URLs
      source: Peer39 published custom-category marketing material
    - scope: per-item
      field: items[]
      limit: 1024
      unit: characters
    - scope: per-category
      field: categoryName
      limit: 120
      unit: characters
      note: exceeding returns error code 42
    - scope: per-category
      field: expirationDate
      limit: 1
      unit: year from today
      note: outside the window returns error code 60 or 62

off_host_note: >-
  The Peer39 MCP Connector beta enforces 60 requests/minute per user with a burst of 10 on
  its /mcp endpoint. That limit belongs to the connector on mcp-connector.scatter-brain.ai
  — a non-Peer39 host — and says nothing about what app.peer39.com enforces.

cross_reference:
  conventions: conventions/peer39-conventions.yml
  errors: errors/peer39-problem-types.yml