Elo Rating

Calculate updated Elo ratings for two players after a match. Supports custom K-factor for different competitive contexts.

⚡ 1 credit per call

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Rating A

Rating B

Outcome

K-Factor (optional, default 32)

Why use this

LLMs can miscalculate Elo deltas, especially around edge cases with unequal ratings or non-standard K-factors. Use this for accurate, deterministic rating updates in games, competitions, or ranking systems.

Input

Field	Type	Required	Description
`rating_a`	number	✓	Current rating of player A
`rating_b`	number	✓	Current rating of player B
`outcome`	`a_wins` \| `b_wins` \| `draw`	✓	Result of the match
`k_factor`	number	—	Sensitivity factor (default 32). Use 16 for established players, 64 for new players

Response

Field	Type	Description
`new_rating_a`	number	Updated rating for player A
`new_rating_b`	number	Updated rating for player B
`delta_a`	number	Points gained or lost by player A
`delta_b`	number	Points gained or lost by player B
`expected_score_a`	number	Player A's expected win probability (0–1)

API Reference

Endpoint

POST https://api.lightningapi.tools/elo-rating

Required headers

Authorization: Bearer <apiKey>
Content-Type: application/json

Example request

{
  "rating_a": 1200,
  "rating_b": 1000,
  "outcome": "a_wins",
  "k_factor": 32
}

Example response

{
  "new_rating_a": 1207,
  "new_rating_b": 993,
  "delta_a": 7,
  "delta_b": -7,
  "expected_score_a": 0.76
}