rescript-schema

ReScript Schema

The fastest composable parser/serializer for ReScript and TypeScript

⚠️ 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:

• Combines validation and transformation without a performance loss
• Can transform parsed value back to the initial format (serializing)
• Works with any Js value, not only Js.Json.t
• Support for asynchronous transformations
• Immutable API with both result and exception-based operations
• Easy to create recursive schema
• Detailed error messages
• Opt-in strict mode for object schema to prevent excessive fields and many more built-in helpers
• Opt-in PPX to generate schema from type
• Works with plain JavaScript/TypeScript too! You don't need to use ReScript
• The fastest composable validation library in the entire JavaScript ecosystem (benchmark)
• Small JS footprint & tree-shakable API (Comparison with Zod and Valibot)

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

• 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@7.0.0	Zod@3.22.2	Valibot@0.32.0
Total size (minified + gzipped)	9.82 kB	14.6 kB	9.88 kB
Example size (minified + gzipped)	4.98 kB	12.9 kB	1.22 B
Nested object parsing	156,244 ops/ms	1,304 ops/ms	3,822 ops/ms
Create schema + Nested object parsing	56 ops/ms	112 ops/ms	2,475 ops/ms
Eval-free	❌	✅	✅
Codegen-free (Doesn't need compiler)	✅	✅	✅
Ecosystem	⭐️	⭐️⭐️⭐️⭐️⭐️	⭐️⭐️⭐️