Q
Query String
Definition
A query string is the part of a URL after the question mark, used to pass extra information to the page.
In plain English
In example.com/shop?colour=blue&size=l, everything after the ? is the query string. It's a list of name=value pairs joined by &.
The page reads those values and changes what it shows — filtering products, remembering a campaign source, jumping to page three of the results.
Why it matters
Query strings are everywhere once you notice them: search results, product filters, pagination, campaign tracking, payment redirects.
They also cause real problems — duplicate content when the same page exists at five URLs, and cache misses that slow a site down. Knowing what they are makes both diagnosable.
How it works
- A ? starts itEverything before the ? is the path.
- Pairs are joined with &key=value&key2=value2, in any order.
- The server or JavaScript reads themAnd responds accordingly.
- Special characters get encodedA space becomes %20 or +.
Nothing private goes in a URL
Query strings land in browser history, server logs and referrer headers. Passwords, tokens and personal data belong in a request body.
Watch it in a real build
Related terms
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