How do I work with JSON in PHP?

Short answer

Use json_encode($data) and json_decode($json, true). Pass JSON_THROW_ON_ERROR so malformed input raises an exception instead of returning null.

php

$data = ['title' => 'Intro to Python', 'views' => 197];

$json = json_encode($data, JSON_THROW_ON_ERROR);
// {"title":"Intro to Python","views":197}

$back = json_decode($json, true, 512, JSON_THROW_ON_ERROR);
// ['title' => 'Intro to Python', 'views' => 197]

#The second argument to json_decode

true returns associative arrays. Omit it and you get stdClass objects, accessed with -> instead of []. Arrays are usually easier to work with in PHP; pick one and be consistent.

#Useful flags

php

json_encode($data,
    JSON_PRETTY_PRINT |          // readable output
    JSON_UNESCAPED_SLASHES |     // / instead of \/
    JSON_UNESCAPED_UNICODE |     // é instead of \u00e9
    JSON_THROW_ON_ERROR
);

Without JSON_THROW_ON_ERROR, both functions return null on failure — and null is also the valid decoding of the input "null". That ambiguity is how JSON bugs hide.

#Sequential arrays vs objects

php

json_encode([1, 2, 3]);              // [1,2,3]      — a JSON array
json_encode([1 => 'a', 2 => 'b']);   // {"1":"a",...} — a JSON object

PHP emits an array only when the keys are 0..n with no gaps. This is why array_filter results often serialise as objects — the keys have holes. Wrap them in array_values().

#Returning JSON from an endpoint

php

header('Content-Type: application/json; charset=utf-8');
echo json_encode($payload, JSON_THROW_ON_ERROR);
exit;

#Reading a JSON request body

php

$body = json_decode(file_get_contents('php://input'), true, 512, JSON_THROW_ON_ERROR);

$_POST is only populated for form encodings. A JSON request body has to be read from the raw input stream.