Can I check a phone number on Substack?

Not directly. Substack can be reached from username. Phone lookups are in beta and cover a small set of platforms.

How fast is a Substack check?

Substack is checked on a full lookup, which streams results as they land - the first matches arrive in around 60 milliseconds and the whole set typically completes in a few seconds.

What happens if Substack blocks the check?

Substack is left out of the response. We never report a platform we could not confirm as "not registered" - a missing platform means unconfirmed, not absent.

Does the API return the Substack account details?

No. You get whether an account exists for the input you sent, and when that was established. No profile contents, photos, followers or private data are collected or returned.

Check if a Substack username is taken

Digital Footprint checks Substack from an username as part of every lookup, alongside 886+ other platforms, breach history and public web mentions - one request, one shape of answer. A hit means an account exists for that input; account contents are never collected.

Accepts: username
Speed: Standard tier
Popularity: #190 by global traffic
Category: Media & publishing

What we check on Substack

Standard tier - checked on every full lookup

Substack is checked from a username. The response says whether that handle exists on Substack - registered: true or registered: false - with the moment that was established in checkedAt. An email address on its own cannot reach Substack; if you only have an email, its local part is tried as a handle and any hit is labelled as derived, never counted as a confirmed match.

Substack is checked on every full lookup (?wait=true or streaming), alongside every other platform. It is not in the sub-second instant subset, which is reserved for the highest-value platforms for each input type.

If Substack blocks the check, times out, or answers ambiguously, it is omitted from results[] entirely rather than returned as registered: false. Absence from the response means "unconfirmed", never "no account".

One request

POST /v1/lookup?wait=true

curl -X POST "https://api.digifootprint.dev/v1/lookup?wait=true" \
  -H "Authorization: Bearer dfp_your_key" \
  -H "Content-Type: application/json" \
  -d '{"query": "someuser"}'

What a Substack result looks like

From results[]

{
  "platform": "substack",
  "registered": true,
  "checkedAt": "2026-08-30T01:50:27.655Z"
}

The full response shape - breaches, web mentions, matches versus socialMatches, and what method means - is in running a lookup.

Related platforms

Every one of these is checked in the same request as Substack.

YouTube Vimeo WordPress Spotify Medium SoundCloud The Guardian Issuu

Substack lookup FAQ

Can I check a phone number on Substack?: Not directly. Substack can be reached from username. Phone lookups are in beta and cover a small set of platforms.
How fast is a Substack check?: Substack is checked on a full lookup, which streams results as they land - the first matches arrive in around 60 milliseconds and the whole set typically completes in a few seconds.
What happens if Substack blocks the check?: Substack is left out of the response. We never report a platform we could not confirm as "not registered" - a missing platform means unconfirmed, not absent.
Does the API return the Substack account details?: No. You get whether an account exists for the input you sent, and when that was established. No profile contents, photos, followers or private data are collected or returned.

Try it free Read the docs