rescript-schema

ReScript Schema 🧬

The fastest parser in the entire JavaScript ecosystem with a focus on small bundle size and top-notch DX.

⚠️ Be aware that rescript-schema uses eval for parsing. It's usually fine but might not work in some environments like Cloudflare Workers or third-party scripts used on pages with the script-src header.

Highlights:

• Works with plain JavaScript, TypeScript, and ReScript. You don't need to use any compiler.
• The fastest parsing and validation library in the entire JavaScript ecosystem (benchmark)
• Small JS footprint & tree-shakable API (Comparison with Zod and Valibot)
• Describe transformations in a schema without a performance loss
• Can reverse transformed values to the initial format (serializing)
• Error messages are detailed and easy to understand
• Support for asynchronous transformations
• Immutable API with both result and exception-based operations
• Easy to create recursive schema
• Opt-in strict mode for object schema to prevent excessive fields. And many more built-in helpers
• Opt-in ReScript PPX to generate schema from type definition

Also, it has declarative API allowing you to use rescript-schema as a building block for other tools, such as:

• rescript-rest - RPC-like client, contract, and server implementation for a pure REST API
• rescript-envsafe - Makes sure you don't accidentally deploy apps with missing or invalid environment variables
• rescript-json-schema - Typesafe JSON schema for ReScript
• Internal form library at Carla

Documentation

• For ReScript users
• For PPX users
• For JS/TS users
• For library maintainers

Comparison

Instead of relying on a few large functions with many methods, rescript-schema follows Valibot's approach, where API design and source code is based on many small and independent functions, each with just a single task. This modular design has several advantages.

For example, this allows a bundler to use the import statements to remove code that is not needed. This way, only the code that is actually used gets into your production build. This can reduce the bundle size by up to 2 times compared to Zod.

Besides the individual bundle size, the overall size of the library is also significantly smaller.

At the same time rescript-schema is the fastest composable validation library in the entire JavaScript ecosystem. This is achieved because of the JIT approach when an ultra optimized validator is created using eval.

	rescript-schema@8.0.0	Zod@3.22.2	Valibot@0.36.0
Total size (minified + gzipped)	9.71 kB	14.6 kB	10.4 kB
Example size (minified + gzipped)	5.48 kB	12.9 kB	1.22 B
Parse with the same schema	155,887 ops/ms	1,273 ops/ms	3,771 ops/ms
Create schema & parse once	146 ops/ms	108 ops/ms	2,485 ops/ms
Eval-free	❌	✅	✅
Codegen-free (Doesn't need compiler)	✅	✅	✅
Ecosystem	⭐️⭐️	⭐️⭐️⭐️⭐️⭐️	⭐️⭐️⭐️