Check if a Substack username is taken

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".

Who checks Substack accounts

Media and publishing accounts are checked because listening, reading and blogging histories are among the oldest footprints a real person leaves. An email that has streamed music or published posts for years behaves like a real customer; one with no media history at all is more often a fresh, single-purpose address.

More on this: Email fraud detection.

Inputs Substack accepts

• Username: send the handle as query. Substack is checked for that exact handle - useful when a person reuses the same name across platforms.

One request

curl -X POST "https://api.digifootprint.dev/v2/lookup?wait=true" \
  -H "Authorization: Bearer dfp_your_key" \
  -H "Content-Type: application/json" \
  -d '{"query": "someuser"}'

What a Substack result looks like

{
  "platform": "substack",
  "registered": true,
  "checkedAt": "2026-10-15T09:53:17.251Z",
  "identity": "username"
}

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.

More media & publishing platforms: SlideShare, Blogger, CNET, Dailymotion, Bandcamp, Goodreads · all media & publishing

Substack lookup FAQ

Can I check a phone number on Substack?

Not directly. Substack can be reached from username. Phone numbers are checked on the messaging and social apps that sign people up by phone.

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.