Poker Hand Evaluator

A collection of useful functions for determining the strongest possible hand given a coordination of cards (hole cards & community cards), the strongest effective hand when comparing two hands, and the probability of winning the hand given what cards are known.

What's new in v4

Version 4 replaces the hand-evaluation core with an integer-based, lookup-table evaluator and rewrites odds to enumerate card combinations instead of permutations. Exact odds calculations are now typically 100× or more faster, and previously infeasible calculations (such as exact preflop odds) complete in well under a second. Breaking changes:

Odds totals are smaller (combination basis). v3 counted every ordering of the unknown cards as a separate scenario; v4 counts every distinct combination once. All percentages are unchanged: every wins/ties/total value is simply divided by a constant factor.
Odds includes an equity field: the hand's share of the pot across all evaluated scenarios (ties split the pot), so each scenario's equities always sum to 1. Prefer equity over wins / total when ties matter.
odds validates its input. Duplicate cards and hands holding more cards than the game allows now throw instead of producing meaningless results.
odds refuses unbounded work. If a calculation would require more than maximumEvaluations hand evaluations (default 500 million), it throws; use simulate instead, or raise the limit.
simulate is now an infinite generator. It samples scenarios with replacement and never exhausts; consumers stop iterating when satisfied. A samplesPerUpdate option controls how many scenarios are evaluated per yield.
A straight-flush detection bug is fixed. v3 could report a flush for hands of 6+ cards containing a straight flush whose lowest card shared a rank with another card (e.g. Kh Qh Jh Th 9h 9d 3s).

Additionally, every failure is now reported as a named error class carrying structured properties rather than a bare Error with a message to parse — see Errors. Code matching on error.message should switch to instanceof checks, as some wordings have changed.

Deprecations

The odds* functions and the Odds* types have been renamed to equity* and Equity*, matching the equity value they report. The old names are still exported as aliases of the new ones and behave identically, but they are marked @deprecated and will be removed in a future major version.

Deprecated	Replacement
`odds`	`equity`
`oddsHoldem`	`equityHoldem`
`oddsOmaha`	`equityOmaha`
`oddsPineapple`	`equityPineapple`
`oddsStud`	`equityStud`
`Odds`	`EquityResult`
`OddsOptions`	`EquityOptions`
`OddsHoldemOptions`	`EquityHoldemOptions`
`OddsOmahaOptions`	`EquityOmahaOptions`
`OddsPineappleOptions`	`EquityPineappleOptions`
`OddsStudOptions`	`EquityStudOptions`

Usage

Types

The following types are defined & utilized by this package.

EvaluatedHand: An object representing the effective hand & strength, given a coordination of cards.
EquityResult: An object representing how a hand will perform given a scenario. Includes the number of wins, ties, and total evaluated outcomes, plus the hand's overall pot equity (between 0 and 1, with tied outcomes contributing a partial share).

Core Functions

`evaluate`

Given a list of hole cards and (optionally) community cards, determine the best possible poker hand and the strength of that hand.

import { evaluate } from '@poker-apprentice/hand-evaluator';
import { HandStrength } from '@poker-apprentice/types';

const result = evaluate({
  holeCards: ['As', 'Qd'],
  communityCard: ['Js', 'Kc', 'Td'],
});

console.log(result);
// => { hand: ['As', 'Kc', 'Qd', 'Js', 'Td'], strength: 6 };

console.log(result.strength === HandStrength.Straight);
// => true

Note that the evaluate does not require 5 cards to determine the best hand. The best hand possible with fewer cards or more cards can be determined as well.

console.log(evaluate({ holeCards: ['As', 'Ad'] }));
// => { hand: ['As', 'Ad'], strength: 9 };

console.log(
  evaluate({
    holeCards: ['9s', '8s'],
    communityCards: ['5d', '6d', '6c', '7c', '2h'],
  }),
);
// => { hand: ['9s', '8s', '7c', '6d', '5d'], strength: 6 };

By default, the evaluate function allows any number of hole cards or community cards to be used when determining the best possible poker hand. If a specific number of hole cards must be used (e.g.: exactly 2 cards in Omaha or up to 2 cards in Pineapple), then the minimumHoleCards and maximumHoleCards options can be provided.

const omahaHand = evaluate({
  holeCards: ['As', 'Kd', 'Td', '2s'],
  communityCards: ['Js', '4s', '3d', '5d', 'Ah'],
  minimumHoleCards: 2,
  maximumHoleCards: 2,
});
console.log(omahaHand);
// => { hand: ['5d', '4s', '3d', '2s', 'As'], strength: 6 }

const pineappleHand = evaluate({
  holeCards: ['Jc', 'Tc', '7d'],
  communityCards: ['9h', '8c', '2d'],
  maximumHoleCards: 2,
});
console.log(pineappleHand);
// => { hand: ['Jc', 'Tc', '9h', '8c', '2d'], strength: 10 }

`compare`

Given two evaluated hands, returns -1, 0, or 1 to represent the stronger hand.

import { compare, evaluate } from '@poker-apprentice/hand-evaluator';

const hand1 = evaluate({ holeCards: ['9s', '8s', '5d', '6d', '6c', '7c', '2h'] });
const hand2 = evaluate({ holeCards: [] });
const result = compare(hand1, hand2);

console.log(result);
// => -1

This function can be used to sort any number of hands in an array.

import { compare, evaluate } from '@poker-apprentice/hand-evaluator';

const communityCards = ['Qs', 'Js', '7d'];
const result = [
  evaluate({ holeCards: ['As', 'Qd'], communityCards }),
  evaluate({ holeCards: ['Ac', 'Tc'], communityCards }),
  evaluate({ holeCards: ['9s', '8s'], communityCards }),
].sort(compare);

`equity`

Given a list of hands and community cards, determine exactly how often each hand will win or tie by exhaustively enumerating every possible combination of the unknown cards (any unspecified hole cards plus the remaining community cards).

Exact enumeration is fast enough for any hold'em scenario, including exact preflop odds, as well as omaha/pineapple/stud scenarios with a typical number of unknown cards. Because the work grows combinatorially with the number of unknown cards, equity throws if a calculation would require more than maximumEvaluations hand evaluations (500 million by default, roughly several seconds of computation); the simulate function handles such scenarios in bounded time instead.

import { Hand, equity } from '@poker-apprentice/hand-evaluator';

const hand1: Hand = ['As', 'Ks'];
const hand2: Hand = ['Jd', 'Jh'];

const result = equity([hand1, hand2], {
  communityCards: ['Qd', 'Js', '8d'],
  expectedCommunityCardCount: 5,
  expectedHoleCardCount: 2,
  minimumHoleCardsUsed: 0,
  maximumHoleCardsUsed: 2,
});

console.log(result);
// => [
//      { wins: 149, ties: 0, total: 990, equity: 0.1505... },
//      { wins: 841, ties: 0, total: 990, equity: 0.8494... },
//    ]

`simulate`

Given a list of hands and community cards, estimate how often each hand will win or tie using a Monte Carlo simulation for roughly estimating the odds of a hand winning or tying.

The simulate generator function returns a generator that yields cumulative results indefinitely; consumers decide when the accumulated sample count (and therefore the accuracy of equity) is sufficient and stop iterating. The accuracy of a Monte Carlo estimate improves with the square root of the sample count: 10,000 samples bound the standard error of equity to about half a percent. An optional samplesPerUpdate option (default 1) controls how many random scenarios are evaluated between yields.

import { Hand, simulate } from '@poker-apprentice/hand-evaluator';

const hand1: Hand = ['As', 'Ks'];
const hand2: Hand = ['Jd', 'Jh'];

const generate = simulate({
  allHoleCards: [hand1, hand2],
  communityCards: ['Qd', 'Js', '8d'],
  expectedCommunityCardCount: 5,
  expectedHoleCardCount: 2,
  minimumHoleCardsUsed: 0,
  maximumHoleCardsUsed: 2,
  samplesPerUpdate: 1000,
});

for (const result of generate) {
  console.log((result[0].equity * 100).toFixed(1), result);
  if (result[0].total >= 3000) {
    break;
  }
}

// => "13.8" [{ wins: 138, ties: 0, total: 1000, equity: 0.138 }, ...]
// => "14.4" [{ wins: 288, ties: 0, total: 2000, equity: 0.144 }, ...]
// => "15.1" [{ wins: 453, ties: 0, total: 3000, equity: 0.151 }, ...]

Helper Functions

In addition to the core functions, there are some poker game-specific functions that wrap these core functions for ease of use. These functions are effectively the same as calling the evaluate or equity function directly with the appropriate option values prepopulated.

The functions also perform appropriate error checking/throwing to ensure that the holeCards and communityCards are of the correct length for each game. See Errors for the classes they throw.

`evaluateHoldem`

Evaluates a hand of Texas Hold'em.

import { evaluateHoldem } from '@poker-apprentice/hand-evaluator';
const hand = evaluateHoldem({
  holeCards: ['As', 'Kd'],
  communityCards: ['9h', '8d', '2c'],
});

`evaluateOmaha`

Evaluates a hand of Omaha.

import { evaluateOmaha } from '@poker-apprentice/hand-evaluator';
const hand = evaluateOmaha({
  holeCards: ['Jc', 'Qd', '4h', '7c'],
  communityCards: ['2c', 'Qs', '4c'],
});

`evaluatePineapple`

Evaluates a hand of Pineapple.

import { evaluatePineapple } from '@poker-apprentice/hand-evaluator';
const hand = evaluatePineapple({
  holeCards: ['Jc', '7h', 'Qh'],
  communityCards: ['9h', '8d', '2c', '3h', 'Td'],
});

`evaluateStud`

Evaluates a hand of Stud.

import { evaluateStud } from '@poker-apprentice/hand-evaluator';
const hand = evaluateStud({ holeCards: ['As', 'Kd', 'Ks', '8s', 'Ac', 'Kh', '4d'] });

`equityHoldem`

Calculates the odds of winning or tying a hand of Texas Hold'em.

import { equityHoldem } from '@poker-apprentice/hand-evaluator';
const allHoleCards = [
  ['As', 'Kd'],
  ['Ks', '8s'],
];
const communityCards = ['Ts', 'Qs', 'Jd'];
const result = equityHoldem(allHoleCards, communityCards);

`equityOmaha`

Calculates the odds of winning or tying a hand of Omaha.

import { equityOmaha } from '@poker-apprentice/hand-evaluator';
const allHoleCards = [
  ['As', 'Kd', 'Td', 'Tc'],
  ['Ks', '8s', '9h', 'Kc'],
];
const communityCards = ['Ts', 'Qs', 'Jd'];
const result = equityOmaha(allHoleCards, communityCards);

`equityPineapple`

Calculates the odds of winning or tying a hand of Pineapple.

import { equityPineapple } from '@poker-apprentice/hand-evaluator';
const allHoleCards = [
  ['As', 'Kd', 'Td'],
  ['Ks', '8s', 'Kc'],
];
const communityCards = ['Ts', 'Qs', 'Jd'];
const result = equityPineapple(allHoleCards, communityCards);

`equityStud`

Calculates the odds of winning or tying a hand of Stud.

import { equityStud } from '@poker-apprentice/hand-evaluator';
const allHoleCards = [
  ['As', 'Kd', 'Ks', '8s', 'Ac'],
  ['9s', '8s', 'Ts', '6s', '4h'],
];
const result = equityStud(allHoleCards);

`simulateHoldem`

Estimates the odds of winning or tying a hand of Texas Hold'em.

import { simulateHoldem } from '@poker-apprentice/hand-evaluator';
const generate = simulateHoldem({
  allHoleCards: [
    ['As', 'Kd'],
    ['Ks', '8s'],
  ],
  communityCards: ['Ts', 'Qs', 'Jd'],
  samplesPerUpdate: 1000,
});
for (const result of generate) {
  console.log(result);
  if (result[0].total >= 10000) {
    break;
  }
}

`simulateOmaha`

Estimates the odds of winning or tying a hand of Omaha.

import { simulateOmaha } from '@poker-apprentice/hand-evaluator';
const generate = simulateOmaha({
  allHoleCards: [
    ['As', 'Kd', 'Td', 'Tc'],
    ['Ks', '8s', '9h', 'Kc'],
  ],
  communityCards: ['Ts', 'Qs', 'Jd'],
  samplesPerUpdate: 1000,
});
for (const result of generate) {
  console.log(result);
  if (result[0].total >= 10000) {
    break;
  }
}

`simulatePineapple`

Estimates the odds of winning or tying a hand of Pineapple.

import { simulatePineapple } from '@poker-apprentice/hand-evaluator';
const generate = simulatePineapple({
  allHoleCards: [
    ['As', 'Kd', 'Td'],
    ['Ks', '8s', 'Kc'],
  ],
  communityCards: ['Ts', 'Qs', 'Jd'],
  samplesPerUpdate: 1000,
});
for (const result of generate) {
  console.log(result);
  if (result[0].total >= 10000) {
    break;
  }
}

`simulateStud`

Estimates the odds of winning or tying a hand of Stud.

import { simulateStud } from '@poker-apprentice/hand-evaluator';
const generate = simulateStud({
  allHoleCards: [
    ['As', 'Kd', 'Ks', '8s', 'Ac'],
    ['9s', '8s', 'Ts', '6s', '4h'],
  ],
  samplesPerUpdate: 1000,
});
for (const result of generate) {
  console.log(result);
  if (result[0].total >= 10000) {
    break;
  }
}

Errors

Every error thrown by this package is an instance of a named class exported from the package root, each carrying structured properties describing the failure. All of them extend HandEvaluatorError, so a single instanceof check distinguishes a problem originating here from any other exception.

import {
  DuplicateCardError,
  HandEvaluatorError,
  MaximumEvaluationsExceededError,
  equityHoldem,
} from '@poker-apprentice/hand-evaluator';

try {
  equityHoldem(allHoleCards, communityCards);
} catch (error) {
  if (error instanceof DuplicateCardError) {
    console.error(`${error.card} was supplied more than once`);
  } else if (error instanceof MaximumEvaluationsExceededError) {
    console.error(`needs ${error.requiredEvaluations} evaluations; use simulate() instead`);
  } else if (error instanceof HandEvaluatorError) {
    console.error(error.message);
  } else {
    throw error;
  }
}

Error	Thrown when	Properties
`HandEvaluatorError`	Never directly; the abstract base class of every error below.	—
`InvalidCardError`	A value that is not a recognized card is supplied.	`card`
`DuplicateCardError`	The same card appears more than once across all hole and community cards.	`card`
`InvalidHoleCardCountError`	More hole cards are supplied than the game allows.	`maximum`, `actual`, `handIndex`
`InvalidCommunityCardCountError`	More community cards are supplied than the game allows.	`maximum`, `actual`
`NoCardsSuppliedError`	`evaluate` is called with neither hole cards nor community cards.	—
`InvalidHoleCardConstraintsError`	`minimumHoleCards`/`maximumHoleCards` contradict each other or the hole cards supplied.	`reason`, `minimumHoleCards`, `maximumHoleCards`, `holeCardCount`
`InsufficientCardsError`	Too few cards are available to form a 5-card hand.	`requiredCount`, `suppliedCount`
`UnsatisfiableHandError`	The hole-card usage rules admit no valid 5-card hand.	`minimumHoleCards`, `maximumHoleCards`, `communityCardCount`
`DeckExhaustedError`	More unknown cards must be dealt than remain in the deck.	`requiredCount`, `remainingCount`
`MaximumEvaluationsExceededError`	`equity` would require more hand evaluations than `maximumEvaluations` permits.	`requiredEvaluations`, `maximumEvaluations`

handIndex is set only by functions accepting multiple hands, and identifies the offending entry in allHoleCards; it is undefined for single-hand functions such as evaluateHoldem.

InsufficientCardsError and UnsatisfiableHandError never escape evaluate, which falls back to describing the best partial hand rather than throwing. They surface from equity and simulate, which require complete 5-card hands.

The reason property of InvalidHoleCardConstraintsError is one of the following string values, typed as HoleCardConstraintViolation:

`reason`	Meaning
`'minimumExceedsSuppliedHoleCards'`	`minimumHoleCards` is greater than the number of hole cards supplied.
`'minimumExceedsMaximum'`	`minimumHoleCards` is greater than `maximumHoleCards`.
`'maximumNotPositive'`	`maximumHoleCards` resolves to zero or less.

Every error also carries a name matching its class name, and accepts a standard cause option, so wrapping and rethrowing works as expected:

throw new InvalidCardError('Xx', { cause: originalError });

Benchmarks

Benchmarked on an Apple M3 Pro MacBook Pro with 36 GB RAM using macOS 26.3. The rank 7-card hands x1000 entry measures the raw integer evaluation core: roughly 18 million 7-card evaluations per second.

┌─────────┬───────────────────────────────────┬─────────────┬────────────────────┬──────────┬─────────┐
│ (index) │ Task Name                         │ ops/sec     │ Average Time (ns)  │ Margin   │ Samples │
├─────────┼───────────────────────────────────┼─────────────┼────────────────────┼──────────┼─────────┤
│ 0       │ 'rank 7-card hands x1000'         │ '18,202'    │ 54936.632827950474 │ '±0.19%' │ 9102    │
│ 1       │ 'evaluate high card'              │ '914,181'   │ 1093.8744429447363 │ '±0.43%' │ 457091  │
│ 2       │ 'evaluate one pair'               │ '823,219'   │ 1214.7421612688306 │ '±0.40%' │ 411610  │
│ 3       │ 'evaluate two pair'               │ '808,347'   │ 1237.092304304102  │ '±0.43%' │ 404174  │
│ 4       │ 'evaluate three of a kind'        │ '843,451'   │ 1185.6051867810047 │ '±0.47%' │ 421726  │
│ 5       │ 'evaluate straight'               │ '928,154'   │ 1077.4070458004828 │ '±0.35%' │ 464078  │
│ 6       │ 'evaluate flush'                  │ '657,305'   │ 1521.3636905792814 │ '±1.32%' │ 328653  │
│ 7       │ 'evaluate full house'             │ '914,105'   │ 1093.9654722760874 │ '±0.57%' │ 457053  │
│ 8       │ 'evaluate four of a kind'         │ '848,706'   │ 1178.2636642995465 │ '±0.73%' │ 424354  │
│ 9       │ 'evaluate straight flush'         │ '937,862'   │ 1066.2542863348142 │ '±0.09%' │ 468932  │
│ 10      │ 'evaluate royal flush'            │ '924,572'   │ 1081.5804035140118 │ '±0.09%' │ 462287  │
│ 11      │ 'equity holdem heads up preflop'  │ '3'         │ 258745033.6        │ '±0.46%' │ 10      │
│ 12      │ 'equity holdem heads up to flop'  │ '6,713'     │ 148946.85403633394 │ '±0.26%' │ 3357    │
│ 13      │ 'equity holdem heads up to turn'  │ '139,049'   │ 7191.69599424761   │ '±0.30%' │ 69525   │
│ 14      │ 'equity holdem heads up to river' │ '1,390,115' │ 719.3646012257714  │ '±0.51%' │ 695058  │
│ 15      │ 'equity holdem multiway preflop'  │ '3'         │ 311137795.8999994  │ '±0.88%' │ 10      │
│ 16      │ 'equity holdem multiway to flop'  │ '4,306'     │ 232224.59582374396 │ '±0.33%' │ 2155    │
│ 17      │ 'equity holdem multiway to turn'  │ '84,077'    │ 11893.760888704976 │ '±0.26%' │ 42039   │
│ 18      │ 'equity holdem multiway to river' │ '1,082,756' │ 923.5685942766954  │ '±0.50%' │ 541379  │
└─────────┴───────────────────────────────────┴─────────────┴────────────────────┴──────────┴─────────┘
equity omaha heads up preflop (single run): 136ms

For comparison, v3 measured 60 ops/sec for equity holdem heads up to flop (now 6,713) and could not complete preflop calculations at all; exact heads-up preflop odds now take under 300ms.

Development

Contributions are welcome. Please create an issue in the project first to discuss any possible enhancements, bugs, or other changes prior to submitting a pull request. Alternatively, browse existing issues if interested in providing a fix.

Environment Setup

Install yarn and git.
Clone this repository: git clone git@github.com:poker-apprentice/hand-evaluator.git
Install dependencies: yarn install

Run tests

To run the full test suite:

yarn test

To run a specific test:

yarn test compare.test.ts           # matches test file name
yarn test -t "compare"              # matches test name/description

Run linter

yarn lint

Run formatter

yarn format

Run benchmarking

yarn benchmark

Regenerate lookup tables

The hand-rank lookup tables in src/core/tables/tables.generated.ts are checked in and rarely need to change. If the generator (scripts/generateTables.ts) is modified, regenerate them with:

yarn generate:tables

The generator validates itself: it asserts the canonical 7,462 hand equivalence classes, their category boundaries and frequencies, and that the perfect hash fills every table slot exactly once.

Build package

yarn build

Name		Name	Last commit message	Last commit date
Latest commit History 57 Commits
.github/workflows		.github/workflows
.vscode		.vscode
bin		bin
scripts		scripts
src		src
.eslintignore		.eslintignore
.eslintrc.js		.eslintrc.js
.gitignore		.gitignore
.prettierignore		.prettierignore
.prettierrc.json		.prettierrc.json
README.md		README.md
babel.config.js		babel.config.js
jest.config.json		jest.config.json
package.json		package.json
rollup.config.js		rollup.config.js
tsconfig.build.json		tsconfig.build.json
tsconfig.json		tsconfig.json
tslint.json		tslint.json
yarn.lock		yarn.lock

Uh oh!

Folders and files

Latest commit

History

Repository files navigation

Poker Hand Evaluator

What's new in v4

Deprecations

Usage

Types

Core Functions

evaluate

compare

equity

simulate

Helper Functions

evaluateHoldem

evaluateOmaha

evaluatePineapple

evaluateStud

equityHoldem

equityOmaha

equityPineapple

equityStud

simulateHoldem

simulateOmaha

simulatePineapple

simulateStud