A lightweight TypeScript library for assertion-based runtime data validation

I was surprised by the source including a bunch of try/catch, which results in deopts for that code path as far as I understand, given that the stated benefit over Zod and other validators was that this should be run in performance critical code. I’d be curious to see benchmarks that show whether this is faster than zod, valibot, and zod4 mini in hot code paths.

Most validation libraries like Zod create deep clones of your data during validation, which can impact performance in high-throughput applications. I built decode-kit to take a different approach: assertion-based validation that validates and narrows TypeScript types in-place, without any copying or transformation. Here's what the API looks like in practice:

import { object, string, number, validate } from "decode-kit";

// Example of untrusted data (e.g., from an API) const input: unknown = { id: 123, name: "Alice" };

// Validate the data (throws if validation fails) validate(input, object({ id: number(), name: string() }));

// `input` is now typed as { id: number; name: string } console.log(input.id, input.name);

When validation fails, decode-kit takes an equally thoughtful approach. Rather than being prescriptive about error formatting, it exposes a structured error system with an AST-like path that precisely indicates where validation failed. It does include a sensible default error message for debugging, but you can also traverse the error path to build whatever error handling approach fits your application - from simple logging to sophisticated user-facing messages.

The library also follows a fail-fast approach, immediately throwing when validation fails, which provides both better performance and clearer error messages by focusing on the first issue encountered.

I'd love to hear your thoughts and feedback on this approach.

The whole benefit over zod seems to be perf, so could you do some benchmarking? I wonder if it’s worth it

arktype does this too!

Love it. I hate zod.