Analyze

Score and improve a cold-email subject line

AI-assisted analysis (with local fallback) returning a 0-100 effectiveness score, issues, strengths, improvement suggestions, and an optional rewritten version of the subject line. This POST is side-effect-free and safe to retry with the same body. Rate limit: 30 requests/minute per IP.

post/api/v1/analyze/subject-line

Request

  • Base URL: https://firstsales.io
  • URL: https://firstsales.io/api/v1/analyze/subject-line
  • Auth: none required

Headers

Idempotency-Keystring

Optional retry key accepted for agent/client compatibility. This analysis operation is side-effect-free, so repeating the same body is safe even without server-side key storage.

Request body

subjectLinestring required

Response

Subject line analysis.

scorenumber required
suggestionsstring[] required
issuesstring[] required
strengthsstring[] required
improvedVersionstring

Changes

No recorded changes to this operation across all 1 revision of this API.