Query String Builder
Build, encode, and decode URL query strings with our free Query String Builder. Add key-value pairs in a clean table interface - values are automatically URL-encoded. Choose from Standard, Form URL-encoded, or Minimal encoding modes to match your use case. Load presets for search queries, UTM campaigns, API pagination, and OAuth auth flows, or import an existing query string to edit it. Copy with or without the leading ? symbol - no signup required.
Build a query string from key-value pairs. Add, remove, and reorder parameters. Values are automatically URL-encoded. Copy the resulting query string or full URL with one click - no signup required.
Why Use Our Query String Builder?
Build Query Strings Visually
Add, remove, and edit key-value pairs in a clean table interface. No need to manually type & and = separators. Each parameter row has a dedicated key and value input with real-time validation and automatic URL-encoding, making it easy to build complex query strings without syntax errors.
Instant Copy & Export
Copy the query string with or without the leading ? symbol with one click. The tool also shows a full URL preview so you can see exactly how the query string will look in context. Perfect for quickly generating tracking links, API calls, and redirect URLs.
Presets & Import from String
Load pre-built presets for common scenarios like search queries, UTM campaign parameters, API pagination, and OAuth2 auth flows. You can also paste an existing query string to import and edit its parameters, making it easy to work with existing URLs.
Multiple Encoding Modes
Choose between Standard (encodeURIComponent), Form URL-encoded (+ for spaces), and Minimal encoding modes. Each mode is suited for different contexts - API calls, form submissions, or browser URLs. See the encoded and decoded views side by side.
Common Use Cases for Query String Builder
API URL Construction
Build REST API request URLs with query parameters for filtering, sorting, pagination, and field selection. Quickly generate API endpoints for testing in tools like Postman, cURL, or directly in your browser, ensuring proper URL-encoding of special characters.
UTM Campaign Link Generation
Create tracking URLs for marketing campaigns with proper UTM parameters (utm_source, utm_medium, utm_campaign, utm_content, utm_term). Use the UTM Campaign preset to ensure consistent tracking across all your marketing channels.
OAuth2 Authorization URLs
Build OAuth2 authorization request URLs with response_type, client_id, redirect_uri, scope, and state parameters. The Auth Flow preset provides a starting point, and the tool ensures all parameters are properly URL-encoded for secure OAuth flows.
Search & Filter Query Building
Construct search and filter queries for e-commerce sites, directories, or data dashboards. Combine category, price range, ratings, sort order, and pagination parameters into a clean, working URL for testing or sharing.
Web Development & Debugging
Build and debug query strings during development. Test how your application handles different parameter combinations, duplicate keys, empty values, and special characters. Import an existing query string to inspect and modify it.
SEO & URL Optimisation
Analyse and optimise URL query parameters for SEO. Ensure parameters are clean, avoid duplicate keys that can confuse crawlers, and generate consistent URL structures for content management systems and e-commerce platforms.
Understanding Query Strings
What is a Query String?
A query string is the part of a URL that appears after the? character. It contains key-value pairs separated by&, used to pass data to web servers, APIs, and applications. For example, in https://example.com/search?q=hello&page=1, the query string is ?q=hello&page=1 where q is the search term and page controls pagination. Query strings are defined in the URL specification (RFC 3986) and are a fundamental part of how the web passes parameters between clients and servers.
How Our Query String Builder Works
- Add parameters:Start by adding key-value pairs to the table. Each row has a key input and a value input. Add as many parameters as you need using the "Add Parameter" button. Remove unwanted parameters with the delete button.
- Choose encoding: Select the encoding mode that matches your use case. Standard mode uses
encodeURIComponent()for strict RFC 3986 compliance. Form URL-encoded mode uses+for spaces (forapplication/x-www-form-urlencoded). Minimal mode only encodes unsafe characters for readability. - Get the result: The query string is built automatically as you type. Copy it with or without the leading
?, view the full URL preview, or use the "Import from String" feature to load an existing query string for editing.
Query String Encoding Explained
URL-encoding (also known as percent-encoding) replaces characters that are not allowed in URLs with a % followed by two hexadecimal digits. The three encoding modes in our tool handle this differently:
- Standard (encodeURIComponent) - Encodes all characters except unreserved characters (A-Z, a-z, 0-9, -, _, ., ~). Spaces become
%20. This is the safest option for API calls and most web applications. - Form URL-encoded - Same as standard but encodes spaces as
+(following theapplication/x-www-form-urlencodedspecification). This is required when mimicking HTML form submissions. - Minimal - Only encodes characters that are definitely not allowed in query strings (
#,&,?,=,%, whitespace). This produces more readable URLs but may not be compatible with all servers.
Privacy, Security & Availability
Our Query String Builder processes everything entirely in your browser. No data is sent to any server - all URL-encoding, parsing, and analysis happens client-side using JavaScript's built-in encodeURIComponent()and decodeURIComponent() functions. The tool is 100% free with no signup, no account, and no usage limits. No cookies, no tracking, and no data collection. Simply load the page and start building query strings immediately.
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Frequently Asked Questions About Query String Builder
A query string is the part of a URL that comes after the ? character, containing key-value pairs separated by &. It is used to pass data to web servers, APIs, and applications. Common uses include search queries (?q=search+term), tracking parameters (?utm_source=newsletter), API filters (?category=electronics&price_max=100), and authentication parameters (?response_type=code&client_id=abc). Query strings are defined in RFC 3986 and supported by every web server and browser.
URL-encoding (percent-encoding) is the process of converting characters that are not allowed in URLs into a safe format. Characters like spaces, &, #, ?, and = must be encoded because they have special meaning in URLs. For example, a space becomes %20 (or + in form encoding), and an & becomes %26. Without proper URL-encoding, query strings can break URLs, cause parsing errors, or introduce security vulnerabilities like parameter injection.
Standard mode uses encodeURIComponent() which encodes all special characters and uses %20 for spaces - this is the safest for most applications. Form URL-encoded mode uses + for spaces, following the application/x-www-form-urlencoded specification used by HTML forms. Minimal mode only encodes the bare-minimum unsafe characters (#, &, ?, =, %), producing more readable URLs but potentially causing issues with some servers.
Yes! Use the "Import from String" mode to paste an existing query string (with or without the leading ?). The tool will parse it and populate the parameter table, where you can add, remove, or modify parameters as needed. This is useful for debugging existing URLs, modifying tracking links, or cleaning up messy query strings.
The tool allows duplicate keys (e.g., category=electronics&category=books), which is valid in query strings and commonly used by APIs. When duplicates are detected, a warning is shown so you can decide whether to keep them or consolidate. Some servers treat duplicate keys as arrays, while others use the last value - our tool supports both scenarios.
No. The Query String Builder runs entirely in your browser using client-side JavaScript. All URL-encoding, parsing, and analysis happens locally on your device. No data is sent to any server, no cookies are set, and no information is logged or stored. You can use the tool completely offline once the page is loaded.
UTM parameters (utm_source, utm_medium, utm_campaign, utm_content, utm_term) are query string parameters used by Google Analytics and other analytics platforms to track the performance of marketing campaigns. They identify where traffic comes from, which marketing channel drove it, and which specific campaign or ad content was clicked. Use the UTM Campaign preset in our tool to get started quickly.
Yes! 100% free with no signup, no account, and no usage limits. Build as many query strings as you need - for APIs, marketing campaigns, development, testing, or any other purpose - completely free, forever, with no restrictions.