pixelmatch

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Introduction

pixelmatch is ‘a small, simple and fast JavaScript pixel-level image comparison library, originally created to compare screenshots in tests’, according to its README. It is only a few hundred lines of code, has no dependencies, and works on raw typed arrays of image data, so it is very fast and runs in Node.js and browsers.

It features accurate anti-aliased pixel detection and a perceptual colour difference metric, and writes a diff image highlighting changed pixels. Many visual testing tools use it as their comparison engine, including jest-image-snapshot and Visual Regression Tracker. A command-line tool is included.

Version 8.0.0 was released in October 2026.

In the quality loop it is a building block for custom visual checks.

The source code is at mapbox/pixelmatch on GitHub under the ISC licence, with about 7,000 stars; the most recent commit was on 6 October 2026.

Features

1. Pixel comparison: Count differing pixels.
2. Anti-aliasing detection: Reduce false positives.
3. Perceptual metric: Colour difference that matches perception.
4. Diff output: Highlight changes.
5. Node and browser: Works on typed arrays.

Pros

1. Tiny and fast: No dependencies.
2. Free to use: Open source under the ISC licence, so the core tool costs nothing to use.
3. Actively maintained: The repository had commits as recent as 6 October 2026.
4. Community: About 7,000 GitHub stars.

Cons

1. Library only: No baseline management or UI.
2. Same-size images: Inputs must match dimensions.

Usage and Links (Example)

import pixelmatch from 'pixelmatch';
const numDiffPixels = pixelmatch(img1, img2, diff, 800, 600, { threshold: 0.1 });

Resources:

• pixelmatch website

Pricing

pixelmatch is free and open source under the ISC licence.

Recommended for?

1. Developers building custom visual checks.
2. Not a fit if you want a full visual testing workflow.

Conclusion

pixelmatch is the standard small library underneath many visual testing tools.

On CheckOps, pixelmatch is filed under the Unit testing and End-to-end & functional stages. Related tools listed here include ODiff, jest-image-snapshot, reg-suit, Visual Regression Tracker, BackstopJS and WebdriverIO Visual Service. Before choosing, compare them on licence, supported languages and platforms, hosting model, and how well each fits your existing CI pipeline. Facts on this page were checked against the official website, documentation and repository on 11 November 2026; statements the vendor makes about its own product are marked as vendor claims.