What is Query String?
Query String is the optional query component after the question mark (?) in a URL. Its exact syntax is application-defined, although web applications commonly interpret it as encoded name-value pairs.
Quick Facts
| Full Name | URL Query String |
|---|---|
| Created | 1994 (RFC 1738 - URL specification) |
| Specification | Official Specification |
How It Works
Syntax and boundaries
RFC 3986 defines the query as the optional URI component between ? and #. Slash and question-mark characters may appear inside it, and the receiving application defines what the data means. A bare flag, repeated name, empty value, or non-pair syntax can therefore be valid for a particular API.
Parsing and encoding
Browser code should parse a complete URL with URL and access its searchParams collection. URLSearchParams preserves repeated entries and serializes data using application/x-www-form-urlencoded rules, where spaces become +. Avoid splitting on & or = by hand, and do not pre-encode values before appending them.
Security and cache behavior
Query data can appear in browser history, server and proxy logs, analytics, copied links, caches, and Referer data permitted by policy. Never place passwords, session tokens, API keys, or personal data in a query string. Validate allowed names and values, apply length limits at the application boundary, and define whether parameter order or tracking fields affect cache keys.
Key Characteristics
- Occupies the optional URL component after ? and before #
- Has application-defined semantics rather than a universal key-value grammar
- Common web form syntax uses encoded names and values separated by &
- Can preserve repeated names and insertion order
- Uses context-specific percent-encoding rules
- May be exposed through history, logs, analytics, caches, and copied URLs
Common Use Cases
- Search engine queries (q=search+term)
- Pagination parameters (page=2&limit=10)
- Filtering and sorting data (?sort=date&order=desc)
- UTM tracking codes for marketing analytics
- Passing state between pages without sessions
Example
Loading code...Frequently Asked Questions
What is the maximum length of a query string?
There is no single cross-platform maximum for a query string. Browsers, clients, servers, proxies, CDNs, and application frameworks can enforce different URL or request-target limits. Define and test an application limit across the complete request path instead of relying on a universal 2,048-character rule.
How do I handle special characters in query strings?
Use a URL-aware API instead of concatenating strings. URLSearchParams accepts decoded names and values, percent-encodes them during serialization, and represents spaces as + under form-encoding rules. encodeURIComponent() is useful for an individual component but does not serialize an entire parameter collection.
What is the difference between query strings and URL fragments?
Query strings (after ?) are sent to the server and used for server-side processing, while URL fragments (after #) are only processed client-side and never sent to the server. Fragments are typically used for in-page navigation or client-side routing in single-page applications.
Can query strings contain arrays or nested objects?
Applications can represent arrays with repeated names, bracket notation, or another documented convention, but the generic URI syntax does not standardize one format. URLSearchParams.getAll() reads repeated names. Client and server code must agree on parsing, ordering, empty values, and validation.
Are query strings secure for sensitive data?
No. HTTPS protects a URL in transit but does not prevent query data from appearing in browser history, logs, analytics, caches, copied links, or Referer data allowed by policy. Keep passwords, session tokens, API keys, and personal data out of URLs and use an authenticated request body or header when appropriate.