Signal Number Lookup API: Check Registration & Identity

Published August 23, 2026

Signal is the messenger of choice for privacy-conscious users, and its adoption keeps growing well beyond that niche. If your product or research touches phone numbers, knowing whether a number is on Signal β€” and being able to resolve its identity β€” can shape how you route messages and enrich contacts. A Signal number lookup API answers both over HTTP.

This guide covers checking Signal registration and looking up a number’s identity.

Step 1 β€” Get an API key

Sign up and copy an active key from your Dashboard. Free credits are included for testing.

Step 2 β€” Check registration

The check operation takes a phone number in international format (digits only) and tells you whether it’s registered on Signal:

curl "https://api.opendata-api.com/api/project/signal/check?key=YOUR_API_KEY&number=15551234567"

Step 3 β€” Look up identity

The user-info operation resolves a registered number to its Signal identity:

curl "https://api.opendata-api.com/api/project/signal/user-info?key=YOUR_API_KEY&number=15551234567"

This is useful when you need a stable per-user identifier rather than just a yes/no on registration.

Use cases

  • Channel routing β€” offer Signal as a contact channel only where it’s actually available.
  • Contact enrichment β€” attach Signal presence/identity to existing phone records.
  • Verification flows β€” confirm a user can be reached on Signal before sending sensitive messages there.
  • List segmentation β€” split audiences by which secure-messaging platforms they use.

Best practices

  • Normalize numbers to E.164 digits (country code, no + or punctuation) before checking.
  • Deduplicate and cache β€” registration status is stable, so avoid re-checking the same number repeatedly.
  • Validate before enriching β€” run check first and only call user-info on registered numbers.
  • Stay compliant β€” process only numbers you have a lawful basis to use, and respect privacy expectations on a privacy-first platform.

Try it

Test lookups on the Signal Number Validation page, or read the check and user-info references. See pricing for per-request costs.