Build an app
The FantasyPros API has a free tier for prototyping. This is the path from an idea to a listing in this directory.
Pick something small enough to finish. The tools that get used solve one problem for one league format like a FAAB pricer, a keeper calculator, a draft board. Breadth can come later.
The FantasyPros public API covers rankings, projections, players, news, and injuries across the supported sports.
Public API documentation ↗There is a free tier for prototyping, and separate paths for personal production and commercial use. Request access through the API product page.
FantasyPros API overview ↗Send your key as a request header and read one endpoint before you build anything around it. Confirm the shape of the response against the docs, not against an example.
Cache aggressively, respect the rate limits, keep the key server-side, credit the data, and handle the error cases. A key in client-side JavaScript is a key you have published.
Ship it somewhere public, then submit the listing. Editors check that the site is live and described accurately, and verify any API claim separately.
Raw NFL data
The FantasyPros API covers rankings, projections and news, but it doesn't include live or past stats. For those, nflverse-data ↗ publishes free NFL datasets as versioned release files: play-by-play, box scores, rosters, schedules, snap counts and participation, going back season by season. It is the usual source for historical stats, updated through the season and readable from any language. Several listed tools are built on it.