Every rule set is transcribed by hand from the governing body's own document (rulebook, handbook, bulletin, or official web page) and stored with its source URL and retrieval date (2026-10-16). Data files: data/rules.json and data/rules.csv.
Calculator math: earliest eligible date = game date + required rest days + 1 (calendar days). New York states rest as "nights" and is converted as days = nights − 1. Innings-based organizations (USSSA) take innings pitched. Consecutive-day, weekly and event caps are shown as warnings.
ArmRules is part of Ground Up Baseball, a small group of free baseball data tools: GloveCode (glove specs and size codes), ArmRules (pitch-count rules), BatCode (bat specs and certifications) and BatRules (which bats each league allows). They share one newsletter.
Rules change. Always confirm with your league, association, or tournament director.