Last Updated: 3/12/2026

Codecs

Codecs provide bidirectional transformations — both encoding (output → input) and decoding (input → output).

Basic Codecs

import * as z from "zod";
 
const Base64Codec = z.codec(
  z.string(), // input type (base64 string)
  z.string(), // output type (plain string)
  {
    decode: (base64) => Buffer.from(base64, "base64").toString("utf-8"),
    encode: (plain) => Buffer.from(plain, "utf-8").toString("base64"),
  }
);
 
const decoded = Base64Codec.parse("SGVsbG8="); // => "Hello"
const encoded = Base64Codec.encode("Hello"); // => "SGVsbG8="

Parsing vs. Encoding

• .parse() / .decode(): Input → Output
• .encode(): Output → Input

codec.parse(input); // decode
codec.decode(input); // same as parse
codec.encode(output); // reverse transformation

Use Cases

Codecs are useful for:

• Serialization formats (JSON, base64, protobuf)
• Data normalization (timestamps, currencies)
• Reversible transformations where you need both directions

Codecs vs. Transforms

• Transforms: One-way (input → output)
• Codecs: Two-way (input ⇄ output)

Use transforms when you only need decoding. Use codecs when you need both directions.

What’s Next

• Transforms — One-way data conversion
• Type Inference — Understand input vs output types