JSON to query string — nested objects and arrays to URL parameters

How to use JSON to query string

1. Paste a JSON object into JSON object. Syntax errors are reported with their line and column.
2. Choose Arrays as: items[0]=a&items[1]=b, items[]=a&items[]=b, items=a&items=b or items=a,b.
3. Tick Percent-encode [ and ] if your target is strict about brackets.
4. Copy the Query string, and use the Key / Value table to check each parameter before encoding.

What it does and when to use it

APIs and search pages often take filters as query parameters: ?filters[size][]=42&page=2. Writing those by hand from a JSON body is slow and easy to get wrong, especially the escaping. Use this tool to build test URLs from a request payload or to check what a client library such as qs should send.

For flat key–value pairs typed one by one, the query string builder is simpler. To encode a single value, use the URL encoder. To read an existing URL back into its parts, use the URL parser.

How it works

The JSON is parsed, then walked depth-first, keeping key order:

• An object key nested under a parent becomes parent[key].
• An array element becomes key[0], key[], a repeated key, or part of one comma-joined value, depending on the option.
• A primitive becomes a pair; null gives an empty value.

Each key and value is then encoded with encodeURIComponent, which follows the RFC 3986 rules. Brackets in keys are put back as [ and ] unless you tick the option. Spaces become %20, not +. Pairs are joined with & and no leading ?. It all runs in your browser.

Worked examples

The default input, arrays as indexes:

{ "q": "running shoes", "page": 2, "filters": { "size": [42, 43], "color": "red" }, "inStock": true }

q=running%20shoes&page=2&filters[size][0]=42&filters[size][1]=43&filters[color]=red&inStock=true

The same input with Arrays as items=a,b and brackets encoded:

q=running%20shoes&page=2&filters%5Bsize%5D=42%2C43&filters%5Bcolor%5D=red&inStock=true

The comma inside the value is encoded too, as %2C.

An array of objects plus special characters, with the repeated-key option:

items[0][id]=1&items[0][qty]=2&note=50%25%20off%20%26%20free

The objects keep their index, and % and & in the note are escaped.

Limits and tips

• Empty arrays and objects vanish. {"tags":[]} produces no parameter at all, so the server cannot tell “empty” from “missing”.
• No types survive. "2" and 2 give the same text. Parse numbers and booleans on the server.
• Long URLs. Big objects can produce URLs that some servers, proxies or browsers refuse. Send large filters in a POST body instead.