TS · correctness

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prefer-zod-parse-output-type

Derive a function's return contract from the local Zod schema whose parsed output it returns.

handWrittenParsedOutput Rule source Tests Catalog JSON

Why

A hand-written contract can drift from the runtime-validated value even while each declaration remains locally valid.

Fix

Export or colocate the schema and derive the contract with z.output<typeof Schema>.

Examples

Before — flagged Do not hand-write the parsed return shape

src/contracts.ts

export interface ParsedRow {
  id: string;
}

src/row.ts

import { z } from "zod";
import type { ParsedRow } from "./contracts.js";
const RowSchema = z.object({ id: z.string() });
function load(): ParsedRow {
  return RowSchema.parse({});
}

After — preferred Derive the validated return contract

src/row.ts

import { z } from "zod";
const RowSchema = z.object({ id: z.string() });
type Row = z.output<typeof RowSchema>;
function load(): Row {
  return RowSchema.parse({});
}