Query String Builder Online — Build & Encode URL Parameters Free

What Is a Query String?

A query string is the part of a URL that comes after the ? character. It consists of key-value pairs separated by &, where keys and values are separated by =. For example, in https://example.com/search?q=hello+world&lang=en&page=1, the query string is q=hello+world&lang=en&page=1.

Query strings are used to pass parameters to web servers: search terms, filters, pagination, authentication tokens, analytics tracking codes, and much more. Building them correctly — with proper encoding — is essential for URLs to work as intended.

How to Use the Query String Builder Online

1. Open the query string builder at DevKits.
2. Enter a base URL (optional) — the tool will append the query string to it.
3. Add key-value pairs using the visual input rows.
4. The tool auto-encodes special characters in keys and values using percent-encoding.
5. Copy the complete URL or just the query string from the output.

Example

Keys/Values:
  q       = "hello world"
  filter  = "date:2026-01-01..2026-03-13"
  sort    = "relevance"

Output query string:
  q=hello%20world&filter=date%3A2026-01-01..2026-03-13&sort=relevance

Key Features

• Visual key-value editor — add, remove, and reorder parameters with an intuitive UI.
• Automatic percent-encoding — special characters are encoded without manual effort.
• Encoding style options — choose between %20 or + for spaces (some APIs require one or the other).
• Base URL integration — combine a base URL with the query string into a complete URL.
• Import from existing URL — paste a URL and extract its existing query parameters for editing.
• Array parameter support — handles repeated keys (tag[]=js&tag[]=css) for APIs that accept arrays.

Use Cases

Building API Request URLs

REST APIs accept parameters via query strings. Building a complex filter URL with multiple parameters — categories, date ranges, sort orders, pagination — is much faster with a visual builder than manual string concatenation. The tool ensures proper encoding every time.

Creating UTM Tracking Links

Marketing campaigns use UTM parameters to track traffic sources. A query string builder makes it easy to construct utm_source, utm_medium, utm_campaign, utm_term, and utm_content parameters consistently across all campaign links.

Testing API Endpoints

When testing an API in Postman or a browser, constructing the right query string manually is error-prone. A builder lets you assemble parameters correctly and copy the complete URL for testing.

Generating OAuth Authorization URLs

OAuth 2.0 authorization URLs require multiple precisely encoded parameters: client_id, redirect_uri, scope, state, and response_type. A query string builder handles the encoding of redirect URIs (which must themselves be percent-encoded) correctly.

URL Encoding Rules

Percent-encoding replaces unsafe characters with % followed by two hex digits. The reserved characters that must be encoded in query string values include: space (%20), & (%26), = (%3D), + (%2B), # (%23), and % itself (%25). The application/x-www-form-urlencoded format (used in HTML forms) encodes spaces as + instead of %20.

Frequently Asked Questions

Should I use %20 or + for spaces in query strings?

Both are valid, but context matters. %20 (strict URL encoding) is universally safe. + (form encoding) is used in HTML form submissions and accepted by most web frameworks. Use %20 when in doubt.

Can query string values contain special characters?

Yes, but they must be percent-encoded. The builder handles this automatically — you type the raw value and it produces the correctly encoded output.

How do I pass an array as a query parameter?

Common conventions include repeated keys (tag=js&tag=css), bracket notation (tag[]=js&tag[]=css), or comma-separated values (tag=js,css). The convention depends on your API or framework. The builder supports all of these styles.

Is there a limit to how many parameters I can add?

The tool has no built-in limit. However, practical URL length limits imposed by browsers and servers are typically 2,000–8,000 characters. The tool warns you if your URL approaches these limits.

Is the tool free?

Yes, completely free. No account required, runs in your browser.