Validation Errors

Errors for input/output validation failures and method mismatches.

Overview

Validation errors are thrown when input parameters fail schema validation, when tool output doesn’t match the expected schema, when an HTTP method doesn’t match, or when a required prompt argument is missing.

Error Reference

InvalidInputError

Thrown when input parameters fail Zod schema validation. This is a public error — validation details are included in the response to help clients fix their requests.

Property	Type	Value
code	string	INVALID_INPUT
statusCode	number	400
isPublic	boolean	true
validationErrors	any	Zod validation error details

new InvalidInputError(message?: string, validationErrors?: any)

Example:

import { InvalidInputError } from '@frontmcp/sdk';

throw new InvalidInputError('Validation failed', {
  field: 'email',
  reason: 'Invalid format',
});

---

InvalidOutputError

Thrown when a tool’s output does not match the declared output schema. This is an internal error — schema details are not exposed to clients.

Property	Type	Value
code	string	INVALID_OUTPUT
statusCode	number	500
isPublic	boolean	false

new InvalidOutputError(errorId?: string)

If a custom errorId (e.g., a request ID) is provided, it is included in the public message for correlation. Otherwise, a generic message is returned.

Example:

import { InvalidOutputError } from '@frontmcp/sdk';

throw new InvalidOutputError('req_abc123');
// Client sees: "Output validation failed. Please contact support with error ID: req_abc123"

---

InvalidMethodError

Thrown when a request uses the wrong HTTP method (e.g., GET instead of POST).

Property	Type	Value
code	string	INVALID_METHOD
statusCode	number	400
isPublic	boolean	true

new InvalidMethodError(method: string, expected: string)

Example:

import { InvalidMethodError } from '@frontmcp/sdk';

throw new InvalidMethodError('GET', 'POST');
// "Invalid method "GET". Expected "POST""

---

MissingPromptArgumentError

Thrown when a required prompt argument is not provided by the caller.

Property	Type	Value
code	string	MISSING_PROMPT_ARGUMENT
statusCode	number	400
isPublic	boolean	true

new MissingPromptArgumentError(argName: string)

Example:

import { MissingPromptArgumentError } from '@frontmcp/sdk';

throw new MissingPromptArgumentError('topic');
// "Missing required argument: topic"