Build URL query strings from key-value pairs with encoding, sorting, and duplicate key handling options.
Type a key and a value on each row and this tool serializes them into a single URL query string, with toggles for percent-encoding, key sorting, and duplicate keys. Pairs are joined with &, keys and values with =. The output is only the query portion - you add the ? prefix and the page or endpoint yourself. The most common surprise is that characters with meaning in a URL (spaces, &, =, #, non-ASCII text) come out percent-encoded, so the resulting string can look nothing like what you typed.
A concrete input and expected output from the current implementation.
Input
q: hello world lang: en-US page: 2
Expected output
q=hello%20world&lang=en-US&page=2
Each row becomes key=value and rows are joined with &. The space in 'hello world' is percent-encoded as %20 because spaces are not allowed raw in a query string; letters, digits, and the hyphen in en-US are unreserved and pass through unchanged. With key sorting enabled the pairs reorder to lang=en-US&page=2&q=hello%20world.
Each row becomes one key=value pair, and pairs are joined with & in the order the rows appear unless sorting is on. An empty value serializes as key= with nothing after the equals sign. Because &, =, and # inside a value would be misread as structure, the tool offers encoding for exactly those characters.
Percent-encoding follows the URL unreserved set: letters, digits, and - . _ ~ stay as-is, while spaces, punctuation, and non-ASCII characters become UTF-8 percent-sequences such as %20 and %C3%A9. Sorting compares keys in code-point order, so uppercase keys sort before lowercase. Duplicate keys either repeat as separate pairs or collapse to the first or last occurrence, per the selected mode.
Because a query string on the wire is ASCII text. Non-ASCII characters are encoded as their UTF-8 bytes with percent prefixes: é is two bytes, C3 A9, hence %C3%A9. A space becomes %20. This is not a bug, and most receivers decode it back automatically. Leave encoding on unless the target endpoint is known to expect raw text.
With duplicate handling set to keep, both pairs survive, as in tag=a&tag=b, which many frameworks parse into an array. With deduplication, either the first or the last occurrence is kept, depending on the mode you pick. The builder can only guarantee what the string contains - how the server resolves repeated keys is up to it.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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