Build API requests, search links, and test URLs without manually placing ampersands or percent escapes. The output updates locally as you type. An optional base URL keeps its existing parameters and fragment while the new query is appended, and nothing you enter is uploaded.
Private browser utility / Developer
Query String Builder
Runs entirely in your browser - no upload, no sign-up.
Query builder
Parameters
Parameter keyParameter valueRow actions
Existing parameters and the # fragment are preserved.
Output options
This option applies when the same key appears more than once.
Live output
0 parameters0 duplicate keys
Query string
Add a parameter to build a query string.Full URL
Add a valid base URL to build the complete link.Add a key and value to start building
What is a query string builder?
A query string builder turns readable key/value rows into the encoded parameters that follow a question mark in a URL. Add duplicate keys for lists, choose the array and space conventions your API expects, and copy either the query string or a complete link without hand-escaping reserved characters.
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How to use
- 01Add parameter rows
Enter each decoded key and value. Repeat the same key on another row when it has multiple values.
- 02Choose the conventions
Select repeated, bracket, or comma array output, then choose <code>%20</code> or plus signs for spaces.
- 03Add a base URL if needed
Leave it blank for only the query string, or enter a complete HTTP or HTTPS URL to build the full link.
- 04Copy the live result
Review the encoded output and copy the query string or complete URL.
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Who it's for
- API developers can assemble filters, pagination, and repeated list parameters in the exact array format an endpoint documents.
- QA engineers can create edge-case URLs with empty values, duplicate keys, Unicode text, and reserved punctuation.
- Technical writers can make copy-ready request examples without accidentally treating an ampersand inside a value as a separator.
- Support teams can append diagnostic parameters to an existing link while preserving its original query and fragment.
FAQ
Is this query string builder free?
Yes. The query string builder is free with no account, download, or usage limit. Add as many parameter rows as you need and the encoded result updates live.
Are my URLs or parameters uploaded?
No. Parameter grouping, encoding, sorting, and URL assembly all run locally in your browser. The tool does not send your keys, values, tokens, or links to a server.
How many query parameters can I add?
The tool does not impose a parameter limit. Real limits depend on the browser, proxy, server, or application that receives the finished URL, so check that system before relying on an unusually long query string.
How do I add an array to a query string?
Enter the same key on multiple rows, then choose the format your API expects. Repeated mode creates <code>tag=a&tag=b</code>, brackets create <code>tag[]=a&tag[]=b</code>, and comma mode creates <code>tag=a,b</code>.
Should spaces use %20 or + in a query string?
Both forms commonly represent spaces in query values. <code>+</code> comes from HTML form encoding, while <code>%20</code> is explicit percent encoding. Literal plus signs are always escaped as <code>%2B</code>, so they are not confused with spaces.
Can the builder keep existing URL parameters?
Yes. Enter a full HTTP or HTTPS base URL and its current query parameters are preserved before the new parameters. A fragment after <code>#</code> also stays at the end of the finished URL.
Are empty query values valid?
Yes. A parameter such as <code>debug=</code> is different from omitting <code>debug</code> completely. Keep empty values when presence has meaning, or turn on Omit empty values when the receiving service treats blanks as noise.