Chance.js

Chance.js is a free, open-source JavaScript library for generating pseudorandom values, including sample data for automated tests. Its generators cover text, people, locations, dates, finance, web data, and other categories. Developers can install it from npm for Node.js or load it in a browser, where they can use a global instance or create multiple instances. The separate chance-cli package offers command-line access to generators and options. Providing a seed when creating an instance makes the generated sequence repeatable; instances with the same seed can produce the same sequence. The integer generator accepts inclusive minimum and maximum bounds, and the unique() helper can create arrays of non-repeating generated items. The documented name generator supports English and Italian nationality options. Chance is distributed under the MIT License, and the site credits Victor Quinn as its writer. Its values are pseudorandom, so the project warns against using them for cryptographic applications that require true randomness.

Chance.js offers a broad set of generators for test data and other sample values, with repeatable output when seeded. Its pseudorandom output rules it out for cryptographic applications requiring true randomness.

Chance.js suits JavaScript developers who need generated sample values for automated tests or other tasks. It is not intended for cryptographic uses that require true randomness.

Chance.js is a free, open-source JavaScript library for creating synthetic values, best suited to developers building test data in Node.js or a browser. Its wide range of generators and repeatable seeded output make it a practical fixture tool; pseudorandomness rules it out for cryptographic uses.

Overview

Chance focuses on generating random strings, numbers, and other sample values for automated tests and similar tasks. Its MIT license and free plan make it accessible for individual developers and teams that want to generate data in code without a paid subscription. The project dates to 2013, and its site credits Victor Quinn as its writer.

The central trade-off is straightforward: Chance provides pseudorandom values that work for test data, but should not be used where an application needs true randomness for cryptographic purposes. It is a strong fit for repeatable test inputs, not a security primitive.

Key features

Generators span basics, text, people, mobile identifiers, web data, locations, time, finance, helper functions, and miscellaneous values. That range covers many common fixture needs in one library. The name generator has a specific boundary: documented nationality options are English and Italian, so it may not suit tests that need names associated with other nationalities.

Instances can be initialized with a seed, allowing the same seed to produce the same sequence of values. That reproducibility helps keep test cases stable and makes a particular generated sequence easier to recreate. The integer generator accepts inclusive minimum and maximum bounds, and unique() can produce an array of non-repeating generated items of a requested length.

In browsers, developers can use a global instance or create multiple instances themselves. The documentation describes loading through Bower, RequireJS, or script tags. For Node.js, Chance installs through npm and can be used in an application; the separate chance-cli package offers command-line generation by generator name with options. The site gives file sizes of 95KB uncompressed for chance.js and 55KB for chance.min.js, or 17KB gzipped, a useful consideration for browser projects watching download size.

Pricing

Chance.js costs nothing under the open-source MIT License. There is no paid tier or free trial to weigh: the free plan is the product. That makes it suitable for individual developers and teams seeking a no-cost generator library, with no paid upgrade required for the described features.

Platforms

Chance supports API and web use. Developers can install it in Node.js with npm or load it in a browser, and the separate CLI package supports command-line use. Its browser file sizes may matter to projects that need to keep client-side assets small.

Who it's for

Chance is aimed at developers who need synthetic data for automated tests, including practical fixtures such as random names and addresses. Seeded instances make it especially useful when a test needs the same generated sequence from run to run. It is less suitable when tests require documented name-nationality options beyond English and Italian, or when the random values serve a cryptographic purpose.

Pros and cons

Pros

• Broad fixture coverage: generators for people, places, dates, finance, web data, and more reduce the need to assemble separate tools for common test values.
• Reproducible sequences: seeds let developers repeat generated output, which supports stable tests and reproducible cases.
• Free and MIT-licensed: the library can be used without a subscription or paid plan.
• Multiple use paths: Node.js, browser loading, and a separate command-line package accommodate different development workflows.

Cons

• Not for cryptography: pseudorandom output cannot serve applications that require true randomness.
• Limited documented name options: nationality support for names covers English and Italian, constraining some test datasets.
• Browser payload: the minified file is 55KB, or 17KB gzipped, which may be a consideration for projects with tight asset budgets.

Alternatives

For a broader comparison, see Test Data Generation Tools. Choose Benerator if you need a free community edition with Linux, macOS, Windows, API, or self-hosted availability; its community edition is single-threaded and has no full graph. dbForge Studio for PostgreSQL is a freemium option with a free trial and an Express plan that includes SQL query history, a visual data editor, and data import and export.

Fishery is another free, MIT-licensed option. Snowfakery is free and open source, with API, Linux, and self-hosted platforms. Tonic Fabricate offers a free tier with $5 monthly credits and a Plus plan at $29 a month with $25 monthly credits and metered additional usage. For a free fake REST API, consider DummyJSON. Faker is a free Python package for self-hosted use, while JSON Schema Faker is an MIT-licensed option available for Linux, macOS, Windows, web, and self-hosted use, with npm and Bun installation.

Verdict

Choose Chance.js when you want a free JavaScript library with broad test-data generators and seeded output that can make test inputs repeatable. Its main advantage is combining those capabilities under an MIT license across Node.js and browser workflows. Look elsewhere if you need cryptographic randomness, or if your test data depends on name-nationality settings beyond its documented English and Italian options.