Query String Builder

The Query String Builder helps you create and inspect the part of a URL that comes after the question mark. It is built for developers, marketers, analysts, QA testers, and support teams who need clean URL parameters for search pages, API calls, redirects, signed URLs, UTM campaigns, and debugging tickets.

How to Use the Query String Builder

1. Choose Build mode when you have key-value pairs, or Decode mode when you already have a query string or URL.
2. In Build mode, enter one key-value pair per line. In Decode mode, paste a raw query string or a full URL.
3. Choose whether spaces should become plus signs or percent-encoded spaces, and choose how repeated keys should be represented.
4. Click Build Query String or Decode Query String to generate the encoded query, decoded table, warnings, and JSON preview.
5. Copy the query string, the question-mark version, the full URL, or the JSON representation for use in code, analytics, APIs, or redirects.

Encoding Notes

Query strings are compact, but small encoding choices matter. A space can be written as + in classic form encoding or as %20 in strict percent encoding. Reserved characters such as &, =, ?, #, and non-ASCII characters should be percent-encoded when they are data rather than URL structure.

Common Uses

• Create UTM campaign URLs without accidentally dropping a parameter.
• Debug API requests that use repeated filters such as tag=python&tag=web.
• Decode redirect URLs, OAuth scopes, search filters, and analytics tags.
• Compare a raw query string with a normalized query string before copying it into code.

FAQ

What is a URL query string?
A URL query string is the part of a URL after the question mark. It stores parameters as key-value pairs, such as q=url+tools&page=2, so browsers, servers, APIs, and analytics tools can pass small pieces of state.

Should spaces be encoded as + or %20?
Use plus signs for classic HTML form query strings and many web application parameters. Use %20 when you need strict percent encoding, signed URLs, API canonicalization, or a style that matches RFC 3986 more closely.

How are repeated query keys handled?
Repeated keys can be kept as tag=one&tag=two, converted to bracket arrays such as tag[]=one&tag[]=two, or converted to indexed arrays such as tag[0]=one&tag[1]=two. Different back-end frameworks prefer different conventions.

Can I paste a full URL into the decoder?
Yes. The decoder extracts the part after the first question mark, ignores the fragment after # for decoding, and shows the normalized query string and decoded parameters.

Does this tool send requests to the URL I enter?
No. The tool only builds, decodes, and displays text. It does not visit the entered URL, call an API endpoint, or validate whether a remote server accepts the parameters.

Why do duplicate and empty query parameters matter?
Duplicate keys and empty values can change how a server interprets a request. Some frameworks turn duplicates into arrays, some keep only the first or last value, and some treat empty values differently from missing parameters.