Web Tools
Query String Builder
Build encoded URL query strings from key-value parameters.
Query parameters
Import existing parameters
Built output
?q=online+tools&tag=web&tag=developerhttps://example.com/search?q=online+tools&tag=web&tag=developer#resultsAbout This Tool
Query strings carry parameters after the ? in a URL and are common in search pages, API requests, filters, pagination, tracking, and debugging. Manually joining keys and values can produce broken URLs when spaces, ampersands, equals signs, Unicode characters, or repeated keys are involved. This builder uses the browser's URL and URLSearchParams behavior to serialize parameters consistently, lets you keep duplicate keys in order, and can attach the result to an optional base URL without sending a network request.
How To Use It
- Optionally enter an absolute HTTP or HTTPS base URL. Existing query parameters on that URL are replaced by the parameters in the builder, while its path and fragment are preserved.
- Add key-value rows in the order you want them serialized. Duplicate keys are allowed because many APIs and web applications intentionally use repeated parameters.
- Use Import to load parameters from an existing query string such as ?tag=one&tag=two or from a complete HTTP/HTTPS URL.
- Copy either the query string by itself or the complete URL. Review the receiving application's parameter rules because this tool handles URL serialization, not application-specific meaning.
Examples
Search text containing spaces
A key q with value hello world becomes ?q=hello+world using URLSearchParams form-style query serialization.
Repeated filters
Two rows named tag with values web and developer remain two ordered tag parameters rather than being silently merged or overwritten.
Reserved characters
Characters such as & and = inside a key or value are percent-encoded so they are data rather than separators in the resulting query string.
Useful Notes
Encoding behavior
The builder delegates serialization to URLSearchParams. In this format, spaces serialize as + and reserved or non-ASCII characters are percent-encoded as needed. This is appropriate for URL query parameter construction and avoids error-prone manual concatenation.
Duplicate keys and order
Query parameter names are not required to be unique. Some servers interpret repeated keys as lists, while others keep the first or last value. The builder preserves your row order and duplicates, but only the receiving application can define their business meaning.
Empty keys and values
A row with an empty value but a non-empty key is preserved, as is a row with an empty key and non-empty value. A completely blank row is ignored. This keeps explicit empty parameters possible without adding separators for unused UI rows.
Base URL behavior
When a base URL is supplied, it must be an absolute HTTP or HTTPS URL without embedded credentials. The generated parameter set replaces its existing query component. A fragment such as #examples remains a fragment and is kept after the new query.
Builder versus URL parser
A URL parser starts with a complete URL and explains its existing components. This builder starts with editable parameter rows and produces a query string or complete URL. The tools complement each other but solve different tasks.
Privacy and network behavior
Building and importing parameters happens locally in browser JavaScript. The tool does not request the generated URL or test the destination server. Avoid putting secrets into URLs unless the target system explicitly requires them, because URLs may be stored in browser history, logs, analytics, or referrer data.
FAQ
Why are spaces shown as plus signs?
URLSearchParams uses application/x-www-form-urlencoded query serialization, where spaces are represented as +. Parsing the query through the same standard converts them back to spaces.
Can I use the same parameter name more than once?
Yes. Duplicate keys are preserved in order. Whether a server treats them as an array, first value, last value, or something else depends on that server or framework.
Does the tool call or validate the destination URL?
No. It validates the base URL's basic HTTP/HTTPS structure and builds text locally, but it does not make a network request or confirm that the destination exists.
What happens to an existing query on the base URL?
It is replaced by the rows currently in the builder. This makes the output predictable and avoids accidentally mixing old and new parameters.
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