Query String ↔ JSON

The part of a URL after the “?” — q=masala+chai&page=2 — carries parameters as names and values. This tool reads a pasted URL or query string into JSON so you can see exactly what a server receives, and builds a correctly encoded query string from a JSON object. Two conventions exist and they disagree, so you choose: the flat rules browsers, fetch and HTML forms use, where a repeated name becomes a list; or the bracket rules of PHP, Rails and Node’s qs, where user[name]=Asha nests an object and tags[]=a builds a list. Decoding follows the WHATWG URL standard to the character, the same code path a browser uses.

1. Choose Query → JSON or JSON → Query, and the dialect your server speaks.
2. Paste a full URL, a query string with or without its “?”, or a JSON object.
3. Read the result. Anything a query string cannot hold exactly — a null, an empty list, a number that will arrive as text — is listed beneath it.
4. Copy the result, or switch direction to convert it back.

• A query string holds only text. Values stay text unless you turn on reading numbers, true/false and null — and even then 007, 1e3 and integers too large for JavaScript stay text, so nothing is changed by rounding.
• In the bracket dialect, the same plain key given twice (a=1&a=2) is refused: PHP keeps the last value and qs makes a list, so there is no single right answer. Use a[]= for a list.
• Keys used in two incompatible ways — a=1 together with a[b]=2, or an index that skips ahead such as a[2] before a[0] — are refused with the key named, rather than silently resolved.
• An empty list or object cannot be written in a query string and is left out, with a note. null is written as an empty value, the same as "".
• Up to 1 MB of input; real servers refuse URLs far shorter than that.
• Everything runs in your browser. URLs often carry tokens and personal details; nothing you paste is uploaded, stored or logged, and no request is made to the address you paste.

Because that is what the form encoding used by query strings means. A literal plus sign is sent as %2B. If you build a URL by hand and type “+” meaning plus, the server reads a space — encoding the value with this tool avoids that.

If it is written in PHP, Ruby on Rails, or Node with Express (which uses qs), it understands brackets. Most other frameworks — and URLSearchParams in the browser — use the flat rules, where only repeating a name makes a list. When unsure, flat is the safe form: every server reads it the same way.

Both decode to a space in a query string. + is what browsers write for forms; %20 is the general URL escape from RFC 3986 and is required in the path part of a URL. Pick whatever the API documentation shows.

Reading it as the number 7 would lose the leading zeros, which matter for PIN codes, account numbers and IDs. Only values that convert to a number and back without any change are read as numbers.