colinhacks/zod · error · Error

Symbols cannot be represented in JSON Schema

Error message

Symbols cannot be represented in JSON Schema

What it means

Thrown by toJSONSchema() when a ZodSymbol schema (z.symbol()) is encountered and unrepresentable is 'throw' (default). Symbols are a JavaScript runtime concept with no JSON or JSON Schema equivalent, so conversion is refused.

Solutions

1. Pass { unrepresentable: 'any' } to toJSONSchema() so symbol fields become {}.
2. Strip symbol fields from the schema used for JSON export; model the external contract with z.string() instead.
3. Split the runtime schema from the export schema so symbols never reach toJSONSchema().

Example fix

// before (throws)
const Schema = z.object({ tag: z.symbol() });
z.toJSONSchema(Schema);

// after
const Schema = z.object({ tag: z.symbol() });
z.toJSONSchema(Schema, { unrepresentable: 'any' });

const opts = schemaContains(schema, (s) => s._zod.def.type === 'symbol')
  ? { unrepresentable: 'any' }
  : {};
const json = z.toJSONSchema(schema, opts);

function hasSymbol(schema) {
  return schema._zod.def.type === 'symbol';
}

try {
  return z.toJSONSchema(schema);
} catch (e) {
  if (e.message === 'Symbols cannot be represented in JSON Schema') {
    return z.toJSONSchema(schema, { unrepresentable: 'any' });
  }
  throw e;
}

When it happens

Trigger: Calling toJSONSchema() on a schema that contains z.symbol(), e.g. a model keyed by Symbol-valued discriminators. Exporting a registry that mixes symbol fields into its type.

Common situations: Internal schemas that use symbols as opaque tokens, then feeding the same schema to a JSON-Schema-based validator or doc generator.

Related errors

• BigInt cannot be represented in JSON Schema
• BigInt literals cannot be represented in JSON Schema
• Custom types cannot be represented in JSON Schema
• Date cannot be represented in JSON Schema
• Dynamic catch values are not supported in JSON Schema

AI-assisted analysis of colinhacks/zod@2d90846af9 (2026-08-11). Data as JSON: /api/errors/05a50cbb8b81626b. Report an issue: GitHub.

Appendix: source

Thrown at packages/zod/src/v4/core/json-schema-processors.ts:110

    json.maximum = maximum;
  }

  if (typeof multipleOf === "number") json.multipleOf = multipleOf;
};

export const booleanProcessor: Processor<schemas.$ZodBoolean> = (_schema, _ctx, json, _params) => {
  (json as JSONSchema.BooleanSchema).type = "boolean";
};

export const bigintProcessor: Processor<schemas.$ZodBigInt> = (_schema, ctx, _json, _params) => {
  if (ctx.unrepresentable === "throw") {
    throw new Error("BigInt cannot be represented in JSON Schema");
  }
};

export const symbolProcessor: Processor<schemas.$ZodSymbol> = (_schema, ctx, _json, _params) => {
  if (ctx.unrepresentable === "throw") {
    throw new Error("Symbols cannot be represented in JSON Schema");
  }
};

export const nullProcessor: Processor<schemas.$ZodNull> = (_schema, ctx, json, _params) => {
  if (ctx.target === "openapi-3.0") {
    json.type = "string";
    json.nullable = true;
    json.enum = [null];
  } else {
    json.type = "null";
  }
};

export const undefinedProcessor: Processor<schemas.$ZodUndefined> = (_schema, ctx, _json, _params) => {
  if (ctx.unrepresentable === "throw") {
    throw new Error("Undefined cannot be represented in JSON Schema");
  }
};

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