Implementation:Microsoft Playwright Validator Primitives

Knowledge Sources	Microsoft_Playwright
Domains	Protocol, Validation
Last Updated	2026-02-12 00:00 GMT

Overview

Concrete tool for validating protocol message parameters and results against a type schema provided by the Playwright library.

Description

The Validator Primitives module defines the foundational building blocks of Playwright's protocol validation system. It exports a `ValidationError` class, a `Validator` function type, a `ValidatorContext` interface, and a global `scheme` registry of named validators. Primitive validators include `tFloat`, `tInt`, `tBoolean`, `tString`, and `tBinary`. Combinators such as `tOptional`, `tArray`, `tObject`, `tEnum`, and `tChannel` allow composing complex validation schemas. The `findValidator` and `maybeFindValidator` functions look up validators by type, method, and kind (Initializer, Event, Params, Result).

Usage

Use Validator Primitives when building or extending protocol validation schemas, or when validating incoming protocol messages on the server or client side of the Playwright RPC channel.

Code Reference

Source Location

• Repository: Microsoft_Playwright
• File: packages/playwright-core/src/protocol/validatorPrimitives.ts

Signature

export class ValidationError extends Error {}
export type Validator = (arg: any, path: string, context: ValidatorContext) => any;
export type ValidatorContext = {
  tChannelImpl: (names: '*' | string[], arg: any, path: string, context: ValidatorContext) => any;
  binary: 'toBase64' | 'fromBase64' | 'buffer';
  isUnderTest: () => boolean;
};
export const scheme: { [key: string]: Validator };
export function findValidator(type: string, method: string, kind: 'Initializer' | 'Event' | 'Params' | 'Result'): Validator;
export function maybeFindValidator(type: string, method: string, kind: 'Initializer' | 'Event' | 'Params' | 'Result'): Validator | undefined;

Import

import { ValidationError, findValidator, scheme, tOptional, tString, tInt } from '../protocol/validatorPrimitives';

I/O Contract

Inputs

Name	Type	Required	Description
arg	any	Yes	The value to validate
path	string	Yes	Dot-separated path describing the location within the message for error reporting
context	ValidatorContext	Yes	Validation context providing channel implementation lookup and binary mode

Outputs

Name	Type	Description
result	any	The validated (and possibly coerced) value, or throws ValidationError

Usage Examples

import { findValidator, scheme, tString, tOptional, tObject } from '../protocol/validatorPrimitives';

// Register a custom validator
scheme['MyTypeMyMethodParams'] = tObject({
  url: tString,
  timeout: tOptional(tInt),
});

// Look up and use a validator
const validator = findValidator('Page', 'goto', 'Params');
const validated = validator(params, 'params', context);

Related Pages

• Environment:Microsoft_Playwright_Node_Runtime_Environment