Frontend Frameworks

PEG.js

Simple parser generator for JavaScript with fast parsers and excellent error reporting.

Status
UnmaintainedNo commits in 2474 days.
Last checked
Aging · Sep 1, 2026
License
Open source
Pricing
Free tier · from $0
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What it is

PEG.js is a simple yet powerful tool that generates parsers from PEG grammars. It produces fast, efficient parsers with detailed error messages, making it ideal for developers working on complex parsing tasks in JavaScript applications.

PEG.js stands out for its simplicity, speed, and detailed error reporting, making it an excellent choice for JavaScript developers who need a robust parser generator without the complexity of larger tools like ANTLR.

When it fits — and when it doesn’t

A good fit for

  • JavaScript developers who need to parse complex grammars efficiently and with clear error messages.

  • Projects requiring custom syntax parsing, such as DSLs or configuration files.

Look elsewhere if

  • Scenarios where a full-fledged parser generator like ANTLR is required due to its more extensive feature set.

  • Real-time data processing tasks that require extremely low latency and high throughput.

Known weaknesses

Each one links to the public issue, changelog or docs page it came from, where we have one.

  1. 01

    Limited integrations with other ecosystems

    Primarily focused on JavaScript, lacks native support for popular build systems and languages outside of JS

  2. 02

    Complex setup for non-trivial grammars

    Defining complex PEG grammars can be intricate and error-prone without extensive documentation or examples

  3. 03

    Performance issues with large input sizes

    Parsers generated by PEG.js may exhibit performance degradation when processing very large inputs due to recursive descent parsing technique

  4. 04

    Documentation lacks depth for advanced use cases

    Official documentation is concise and might not cover all nuances of advanced grammar design or optimization techniques

What it does well

  • Generates fast parsers from PEG grammars

  • Provides excellent error reporting for easier debugging

  • Simple and easy to use API

  • Supports JavaScript ES6+ features

  • Highly customizable parser generation options

Pricing

Free tier
YesOpen source — free to use
Paid from
$0
Model
Flat rate
Enterprise plan
No

Pricing not independently confirmed — check the vendor’s page.

Performance benchmarks

How Fast Is It?

Set up PEG.js

Setup steps, common gotchas and what to check after 30 days.

Open the setup guide →