Every other guide about finding a league ID tells you to open the platform and read it off the URL. That advice is useless here, because the platform is gone: fantasy.nfl.com redirects every URL to a news index, and there is no page left that will tell you your league's number.
There is also no lookup by username. The endpoint that would have listed the leagues an account belonged to is one of the ones still requiring a developer key, so nobody can search for your league on your behalf. The ID has to come out of your own records.
The good news is that it was in a URL for years, and URLs leave traces in more places than people expect.
What you are looking for
The league ID was the number in the path of every page of your league:
https://fantasy.nfl.com/league/1234567
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your league IDIt is a plain integer and it is short — commonly six or seven digits, sometimes fewer for very old leagues. It does not change from season to season, which is the one convenience in this whole situation: one number covers your league's entire history. If you are used to Sleeper's eighteen-digit IDs, this will look too short to be real. It is real.
Six places the number still survives
1. Your browser history
The most likely hit by a wide margin, if you played in the last year or two. Open your history and search for fantasy.nfl.com — the results still contain the full URLs even though the pages no longer load.
- Chrome or Edge: Ctrl+H, or Cmd+Y on a Mac, then search fantasy.nfl.com.
- Safari: History, then Show All History, and search the same term.
- Firefox: Ctrl+Shift+H for the library, then search.
History is usually kept for around three months in Chrome, so this route closes over time. It is the first thing to try and the first thing to lose.
2. Your bookmarks
Anyone who checked their team daily for a decade probably bookmarked it. Search your bookmarks for nfl.com or for the league's name.
3. Old email from NFL Fantasy
This is the route that works when history has already rolled over, and it reaches much further back. NFL Fantasy sent a lot of mail — league invitations, draft reminders, trade and waiver notifications, weekly recaps — and those messages linked straight into the league.
Search your mail for "NFL Fantasy" or for fantasy.nfl.com, open anything from the right league, and read the link target rather than clicking it. The link will redirect; the number in it is still good.
4. The group chat
Every league has one, and somebody pasted a league link into it — usually attached to an argument about a trade. Search it for nfl.com.
5. A leaguemate
The ID is the same for everyone in the league, so any of the eleven other managers looking through their own history or mail solves it for all of you. This is worth asking in the group chat before spending an hour on your own archaeology.
6. Your ESPN league, if the migration ran
A league that was imported to ESPN kept its records but got a new ESPN league ID; the two are different numbers. Worth checking the ESPN league's history and settings pages anyway — and worth remembering that what ESPN shows you is what the migration managed to carry, which is not always everything.
Checking you have the right number
You do not have to guess. Put the ID into the rescue tool and it either comes back with your league's name and your own team names, season by season, or it tells you there is nothing there. Team names are the tell — they are unmistakable to anyone who was in the league, and they are the fastest confirmation you have the right league rather than a stranger's.
If you cannot find it at all
Then the ESPN migration is your remaining route, and it depends on whether your league manager ran it. Failing that, what your league remembers between the twelve of you is what is left — which is exactly the argument for writing the finishing order of every season down somewhere that does not belong to a platform.