This site uses a classic Elo framework with MMA-specific tuning.
Official published parameters:
Starting Elo: 1000
Base K: 40
KO/TKO/Sub multiplier: 1.15x
Each fight computes expected win probability from both fighters' current Elo. A win moves ratings by K-scaled surprise: upset wins gain more, expected wins gain less.
Try your own parameters (computed in your browser from the full fight timeline; nothing is sent to the server).