jq Playground

How it works

jq Quick Reference

Tips & Tricks

Code Examples

const jq = await import('jq-web');
const data = { users: [{ name: 'Alice', age: 30 }, { name: 'Bob', age: 25 }] };
const names = jq.json(data, '[.users[].name]');
console.log(names); // ["Alice", "Bob"]

# Install jq (macOS)
brew install jq

# Filter from file
jq '.users[].name' data.json

# Filter from stdin
curl -s api.example.com/users | jq '.[0].email'

# Select and transform
jq '[.items[] | select(.active) | {id, name}]' data.json

import subprocess, json

data = json.dumps({"users": [{"name": "Alice"}, {"name": "Bob"}]})
result = subprocess.run(
    ["jq", "[.users[].name]"],
    input=data, capture_output=True, text=True
)
print(result.stdout)  # ["Alice","Bob"]

Frequently Asked Questions

What is jq?

jq is a lightweight, command-line JSON processor. It lets you slice, filter, map, and transform JSON data using a simple expression language. jq is commonly used in shell scripts to process API responses, extract fields from JSON files, and reshape data before passing it to other tools.

What is jq used for?

jq is used to query and transform JSON from the command line or in scripts. Common uses include extracting specific fields from API responses (curl ... | jq '.data[].id'), filtering arrays by a condition, reshaping objects into a new structure, and pretty-printing JSON for readability.

What does . mean in jq?

A single dot (.) is the identity filter — it outputs the input unchanged. It is also used to access object fields: .name returns the value of the name key, and .user.email chains field access to reach nested values.

How do I filter an array with jq?

Use .[] to iterate over array elements, then pipe to select() to filter: .items[] | select(.active == true). Wrap in brackets to collect results back into an array: [.items[] | select(.active == true)].

How do I extract a field from every object in an array?

Use the iterator and field access together: [.users[].name] collects the name field from every object in the users array into a new array. Without the brackets, .users[].name streams each value as a separate output line.

What is the difference between .[] and .[n] in jq?

.[] iterates over all elements of an array or all values of an object. .[n] accesses a single element by index — .[0] returns the first element, .[-1] returns the last.

How do I reshape JSON with jq?

Use object construction syntax: {id: .id, fullName: (.first_name + " " + .last_name)} builds a new object. Combined with the array iterator, [.users[] | {id, name}] maps an array to a new structure.

Is my data sent to a server?

No. All jq processing runs entirely in your browser using a WebAssembly build of jq. Your JSON data never leaves your machine and no account or installation is required.

What version of jq does this playground support?

The playground uses jq-web 0.6, compiled from jq 1.6 source via Emscripten/WebAssembly. It supports the full jq 1.6 filter language including select, map, reduce, path, and all built-in functions.

How do I handle null values in jq?

Use the alternative operator // to provide a default: .name // "Unknown" returns "Unknown" if name is null or absent. select(. != null) removes null values from a stream.

How do I count items in jq?

Use the length built-in: .items | length returns the number of elements. For filtered counts: [.items[] | select(.active)] | length.

How do I sort and group with jq?

sort_by(.field) sorts an array by a field. group_by(.category) groups elements into sub-arrays by a shared field. Add | reverse after sort_by for descending order.

Related Tools

Other free developer tools available on DevFormatter.