webonyx/graphql-php is a comprehensive PHP implementation of the GraphQL specification, serving as a server-side library for parsing, validating, and executing GraphQL queries. It provides a full type system (ObjectType, InterfaceType, UnionType, EnumType, InputObjectType, ScalarType), a recursive-descent parser, an AST visitor infrastructure, a query validator with over 30 validation rules, and a reference executor that mirrors the GraphQL.js implementation. The library also includes a PSR-7-compatible server layer (StandardServer) for handling HTTP requests, along with optional promise adapters for async execution via ReactPHP or Amp. The architecture is library-oriented: clients build schemas programmatically or from SDL via BuildSchema, then execute queries through GraphQL::executeQuery() or the StandardServer. The type system uses lazy initialization (closures/callables) to handle circular references, and a type loader enables deferred schema composition. Notable design patterns include a rich AST visitor with enter/leave operations (including skip, stop, remove, edit), a synchronous promise adapter that enables DataLoader-like batching in synchronous PHP, and a modular validation rule system where each rule is a standalone visitor. The codebase demonstrates high craftsmanship with heavy use of static analysis (PHPStan), extensive unit tests ported from graphql-js, and performance benchmarks. While it is a port of the JavaScript reference implementation, it introduces PHP-idiomatic features such as attribute-based annotations (#[Description], #[Deprecated]) and per-schema scalar overrides.