graphql.php

<?php

require_once __DIR__.'/vendor/autoload.php';

use GraphQL\Type\Definition\ObjectType;
use GraphQL\Type\Definition\Type;
use GraphQL\Schema;
use GraphQL\GraphQL;

$queryType = new ObjectType([
    'name' => 'Query',
    'fields' => [
        'echo' => [
            'type' => Type::string(),
            'args' => [
                'message' => ['type' => Type::string()],
            ],
            'resolve' => function ($root, $args) {
                return $root['prefix'].$args['message'];
            }
        ],
    ],
]);

$mutationType = new ObjectType([
    'name' => 'Calc',
    'fields' => [
        'sum' => [
            'type' => Type::int(),
            'args' => [
                'x' => ['type' => Type::int()],
                'y' => ['type' => Type::int()],
            ],
            'resolve' => function ($root, $args) {
                return $args['x'] + $args['y'];
            },
        ],
    ],
]);

$schema = new Schema([
    'query' => $queryType,
    'mutation' => $mutationType,
]);

$rawInput = file_get_contents('php://input');

try {
    $rootValue = ['prefix' => 'You said: '];
    $result = GraphQL::execute($schema, $rawInput, $rootValue);
} catch (\Exception $e) {
    $result = [
        'error' => [
            'message' => $e->getMessage()
        ]
    ];
}

header('Content-Type: application/json; charset=UTF-8');
echo json_encode($result);

php -S localhost:8000 graphql.php
curl http://localhost:8000 -d "query { echo(message: \"Hello\") }"
curl http://localhost:8000 -d "mutation { sum(x: 2, y: 2) }"