Query String Parser
Parse any URL query string into structured key-value pairs. Our tool automatically URL-decodes values, detects duplicate keys, highlights bracket notation (user[name]) and array notation (ids[]), and provides a formatted JSON representation - all with one click. Perfect for API debugging, URL analysis, and web development. Fully private and 100% free.
Parse any query string into structured key-value pairs. Automatically URL-decodes values, detects duplicate keys, highlights bracket/array notation, and generates a JSON representation.
Enter a query string (with or without leading ?). Press Ctrl+Enter (or Cmd+Enter) to parse.
Why Use Our Query String Parser?
Instant Query String Parsing
Paste any query string and instantly parse it into structured key-value pairs. Supports both ?prefixed and raw query strings, automatically URL-decodes all values, and displays results in a clean, sortable table with decoded and raw values side-by-side.
Duplicate Key & Anomaly Detection
Automatically detects duplicate parameter keys, highlights them with warning badges, and explains how different server-side frameworks handle duplicates. Also identifies bracket notation (user[name]) and array notation (ids[]) with colour-coded indicators.
JSON Output & Export
View the parsed query string as a formatted JSON object with one click. The JSON representation converts parameters to key-value pairs (or arrays for duplicate keys), making it easy to use the parsed data in your JavaScript, Python, or any programming language.
Comprehensive Parameter Details
Each parameter shows its decoded key, decoded value, raw key, and raw value. Expand any row to see the full raw key-value pair with one-click copy. Summary stats show total parameters, unique keys, duplicate count, and character length at a glance.
Common Use Cases for Query String Parser
API Debugging & Testing
When debugging API requests, use the Query String Parser to inspect query parameters sent to endpoints. Quickly identify malformed parameters, encoding issues, or unexpected duplicate keys that could cause backend processing errors.
Frontend Development
Frontend developers can parse and inspect query strings from URL parameters to understand the data structure being passed between pages. The JSON output makes it easy to copy parsed parameters into JavaScript objects for testing.
URL Analysis & Forensics
Security researchers and analysts can use the parser to examine suspicious URLs for tracking parameters, hidden identifiers, or analytics tags. The duplicate and anomaly detection helps identify unusual parameter patterns.
UTM Campaign Verification
Marketing professionals can verify UTM campaign parameters in tracking URLs. Parse the query string to confirm utm_source, utm_medium, utm_campaign, utm_term, and utm_content are correctly formatted and URL-encoded.
Web Analytics Parameter Audit
Audit the query parameters being passed to your analytics platform. Identify redundant parameters, check for proper encoding, and ensure PII or sensitive data is not being inadvertently exposed in URL query strings.
Learning URL & HTTP Fundamentals
Students learning web development can explore how query strings work by parsing real-world examples. Understand URL encoding, the difference between & and ; separators, and how duplicate keys are handled by different frameworks.
Understanding Query Strings
What is a Query String?
A query string is the portion of a URL that appears after the ? (question mark) character. It contains key-value pairs that pass data to web applications, APIs, and analytics platforms. The standard format is key=value pairs separated by & characters. For example, in the URL https://example.com/search?q=hello&page=1, the query string is q=hello&page=1. Query strings are defined in RFC 3986 (Uniform Resource Identifier) and are widely used across the web for search parameters, API filters, tracking codes, pagination, and form data.
How Our Query String Parser Works
- Enter a Query String: Paste any query string, with or without the leading ? character. The tool also accepts semicolons (;) as separators, which are valid per the application/x-www-form-urlencoded specification.
- Parsing & Decoding: The query string is split into individual key-value pairs. Each key and value is URL-decoded to reveal the original text. Percent-encoded sequences (%20 for space, %2B for +, etc.) are converted to their human-readable characters using JavaScript's decodeURIComponent.
- Analysis & Output: Each parameter is analysed for duplicate keys, bracket notation (e.g., user[name]), and encoded characters. The results are displayed in an interactive table with expandable rows, summary statistics, and a formatted JSON representation for easy copying.
Query String Encoding & Best Practices
- URL Encoding: Special characters in query strings must be percent-encoded. Spaces become %20 or +, non-ASCII characters are encoded as their UTF-8 byte sequences (e.g., ü → %C3%BC), and reserved characters like & and # must also be encoded.
- Duplicate Keys: Different server frameworks handle duplicate keys differently. PHP and Rails create arrays from duplicate keys (using[] notation), while Express.js and ASP.NET typically take the last value. Understanding how your framework handles duplicates is critical.
- Nested Parameters: Many frameworks support nested parameter notation using brackets, e.g.,
user[name]=John&user[age]=30. This creates a nested structure that our parser identifies and highlights. - Maximum Length: While there is no formal limit in the HTTP specification, most servers and CDNs impose a maximum URL length (typically 8 KB to 64 KB). Browsers also have limits - Internet Explorer capped URLs at 2,083 characters, while modern browsers support much longer URLs.
Privacy, Security & Availability
Our Query String Parser processes everything locally in your browser. No query strings, URLs, or parameter data are sent to any server, stored in any database, or logged in any way. All parsing and analysis happens entirely client-side using JavaScript. The tool is 100% free with no signup, no account, and no usage limits. Whether you are parsing a simple tracking URL or a complex API query string, your data never leaves your device.
Related Tools
DNS Propagation Checker
Check if DNS changes have propagated by querying multiple global nameservers (Cloudflare, Google, Quad9). Shows propagation status across regions with live results and colour-coded status indicators - free online DNS propagation checker.
Domain Age Checker
Check the age of any domain in years, months, weeks, and days. Enter a domain name to get its creation date, registration timeline, registrar info, and SEO authority estimate based on domain age - all fetched from the official RDAP registry in real time. Free online domain age checker.
Bulk WHOIS Lookup
Check domain registration information for up to 20 domains at once using the RDAP protocol. View registrar, creation date, expiry date, nameservers, and domain status codes in a sortable table - free online bulk WHOIS lookup.
Domain Expiry Checker
Check when any domain expires - enter a domain name to see its expiration date, days remaining, registrar lock status, auto-renew status, and complete WHOIS details. Colour-coded health indicators show whether renewal is urgent. Free online domain expiry checker.
Frequently Asked Questions About Query String Parser
A query string is the part of a URL that comes after the ? character, containing key-value pairs separated by & characters. It is used to pass parameters to web pages and APIs, such as search queries, filter options, pagination settings, and tracking codes.
Paste a query string into the input field and click "Parse Query String". The tool splits the string into individual key-value pairs, URL-decodes each component, and displays them in a structured table. It also detects duplicate keys, bracket notation, and encoded characters, and generates a JSON representation of the parsed data.
No. The tool handles both formats - with or without the leading ? character. Simply paste the query string as you have it, and the parser will automatically strip the ? if present.
The tool handles standard URL percent-encoding (e.g., %20 for space, %2B for +). It also decodes + characters as spaces (as per application/x-www-form-urlencoded convention). All decoding uses JavaScript's decodeURIComponent for accuracy.
The tool detects and highlights duplicate keys with a warning badge. In the parsed table, each parameter is shown separately. The JSON output converts duplicate keys into arrays. The actual handling of duplicates depends on the server-side framework - PHP and Rails preserve all values as arrays, while Express.js typically uses the last value.
Absolutely. All parsing happens locally in your browser. No data is sent to any server, stored, or logged. Your query strings and the data they contain remain completely private on your device.
Yes. Each individual parameter pair can be copied with a click. The JSON representation can be copied in full. You can also expand any parameter row to see the raw key and value with their own copy buttons.
Yes! 100% free with no signup, no account, and no usage limits. Parse as many query strings as you need, as often as you need. All processing happens locally in your browser with complete privacy.