Hunter

Hunter.io is narrowly focused on email finding and verification — it does this well and doesn't try to be a full enrichment platform. The three core APIs are Domain Search (find email addresses associated with a domain), Email Finder (find a specific person's email given name + domain), and Email Verifier (validate an email address). For agents, this focused scope is valuable when the specific need is email discovery or verification rather than full contact enrichment. The free tier (25 searches/month) enables testing. The data source is primarily web-crawled and pattern-inferred email addresses. Agents building outreach automation, CRM enrichment, or contact verification workflows find Hunter's API straightforward to integrate. The limitation: it's email-only — no phone numbers, no firmographic data, no intent signals.

API key authentication via api_key query parameter. Keys are generated in the Hunter.io dashboard. One key per account with full API access — no scoping. No OAuth for third-party apps. Free tier provides 25 requests/month; paid plans scale up. Each API operation consumes one credit (domain search, email find, or email verification). Agents must track credit consumption to avoid exhaustion. The API returns remaining credits in the X-RateLimit-Remaining header. No temporary credentials or key rotation mechanism. For agents, the main consideration is credit budgeting: agents processing many contacts should estimate credit needs against their plan. Bulk verification is more credit-efficient than individual calls for large lists.

API documentation at hunter.io/api-documentation/v2 is clean, complete, and easy to navigate. Every endpoint is documented with parameters, response examples, and error codes. The documentation includes a Google Sheets add-on guide for non-developer access. Client libraries exist for Python (pyhunter), Node, Ruby, Go, and PHP — mostly community-maintained. The API's simplicity means the documentation surface is small and digestible — agents can read the entire API reference in 15 minutes. Integration guides for CRM platforms and Zapier provide no-code alternatives. The documentation accurately represents the API's scope — no feature inflation. For agents with email-specific needs, Hunter's focused documentation enables the fastest path from reading to production of any enrichment API.

REST API at api.hunter.io/v2/ with clean GET-based endpoints. Domain Search: GET /domain-search?domain={domain} returns email addresses, patterns, and department information. Email Finder: GET /email-finder?domain={domain}&first_name={name}&last_name={name} returns the most likely email and confidence score. Email Verifier: GET /email-verifier?email={email} returns deliverability status (valid, invalid, accept_all, unknown), MX record verification, and format validation. Response payloads are clean JSON with confidence scores. The API design is REST-idiomatic: GET for reads, POST for bulk operations. Bulk verification accepts CSV upload for batch processing. Account endpoint returns credit balance. The API surface is small and well-designed — agents can integrate all three endpoints in an hour.

API errors return JSON with errors[] array containing id, code, and detail fields. Error codes are descriptive: invalid_api_key, missing_parameter, rate_limit_exceeded. Rate limits are per-second (10 requests/second for most plans). The Email Verifier returns a confidence score and status — agents should handle 'accept_all' and 'unknown' statuses appropriately (accept_all means the server accepts any email, not that the specific address exists). Email Finder confidence scores range from 0-100 — agents should set a minimum confidence threshold for usability. Domain Search may return 0 results for small or privacy-focused companies. The API is reliable and predictable — errors are clear, and the scope is narrow enough that edge cases are well-understood.