Query string builder — encode key=value pairs into a URL, or decode one

How to use the query string builder

1. Leave Mode on Build.
2. In the text box, write one key=value per line. Only the first = splits the line, so values may contain more = signs. A line without = becomes key= with an empty value.
3. Add a Base URL (optional). If it already has a ?, the new pairs are joined with &.
4. Pick Encode spaces as %20 or + (form style).
5. Copy the full URL, or check each pair in the Encoded pairs table. To read a query instead, switch Mode to Parse and paste a URL or query string.

What it does and when to use it

Hand-written query strings break in small ways: an & inside a value starts a new parameter, a # cuts the URL short, and a + becomes a space on arrival. The builder encodes every key and value, so the server receives exactly what you typed. Use it to build a search link for a test, a redirect URL with a nested return URL, or a request to paste into a cURL to Code command.

Parse mode does the reverse for a URL copied from a browser or a log. You get a Key/Value table plus a JSON object, with repeated keys collected into an array.

How it works

Each key and value goes through JavaScript’s encodeURIComponent, which leaves letters, digits and - _ . ! ~ * ' ( ) as they are and percent-encodes everything else as UTF-8 bytes. With the + option, every %20 is then replaced with +. Pairs are joined with & and prefixed with ?. Parse mode drops everything up to the first ? and from the first #, then decodes the rest with URLSearchParams, the browser’s form-decoding rules.

Worked examples

A search link. The default lines with base https://shop.example.com/search and %20:

https://shop.example.com/search?q=running%20shoes&size=42&color=red&color=blue&sort=price%3Aasc

The colon in price:asc became %3A, and both colours are kept.

A nested return URL. Lines redirect=https://app.example.com/cb?x=1&y=2 and email=ana+test@example.com, spaces as +, no base:

?redirect=https%3A%2F%2Fapp.example.com%2Fcb%3Fx%3D1%26y%3D2&email=ana%2Btest%40example.com

Without encoding, the server would see y=2 as its own parameter and the email as “ana test”.

Parsing. …/search?q=running+shoes&color=red&color=blue&empty=#results gives rows such as q | running shoes, and the JSON turns color into an array of "red" and "blue", with "empty": "".

Limits and tips

• A #fragment in the base URL is kept at the end, so …/p#top becomes …/p?a=1#top.
• It does not sort, remove duplicates or check keys against an API.
• To escape text for other places, such as JSON or shell, use the String Escaper. To inspect the finished link, paste it into the URL Parser.