Redirecting & Rewriting URLs
Discover how to redirect network requests to different URLs or rewrite parts of URLs based on defined criteria.
Redirecting & Rewriting URLs is a free Browser Extensions Development (Chrome & Edge) lesson on CoddyKit — lesson 3 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Browser Extensions Development (Chrome & Edge) learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Intro to URL Magic
Welcome! In this lesson, we'll learn how browser extensions can change where network requests go or how their URLs look.
- Redirecting sends a request to a completely different URL.
- Rewriting modifies parts of the original URL before it's processed.
Both are powerful tools for controlling web traffic using the `declarativeNetRequest` API.
Why Redirect or Rewrite?
Modifying URLs can serve many useful purposes:
- Enforce HTTPS: Automatically upgrade insecure HTTP connections.
- Fix broken links: Redirect old URLs to new ones.
- Clean up URLs: Remove unnecessary tracking parameters.
- Block unwanted content: Redirect specific requests to an empty page.
It helps improve security, privacy, and user experience.
The `redirect` Action Type
To redirect a network request, we use the `redirect` action type in our `declarativeNetRequest` rules. This action specifies a new URL or a pattern to generate one.
Here's a basic structure for a redirect rule:
{
"id": 1,
"priority": 1,
"action": {
"type": "redirect",
"redirect": {
"url": "https://new-example.com"
}
},
"condition": {
"urlFilter": "https://old-example.com/*"
}
}Simple URL Redirect Example
Let's say you want to redirect all requests to an old blog post URL to a new one. This rule tells the browser: 'If you see a request for old-blog.html, send it to new-blog-post.html instead.'
[
{
"id": 1,
"priority": 1,
"action": {
"type": "redirect",
"redirect": {
"url": "https://www.example.com/new-blog-post.html"
}
},
"condition": {
"urlFilter": "https://www.example.com/old-blog.html"
}
}
]Enforcing HTTPS with Redirects
A common use case is to ensure secure connections. You can redirect all HTTP requests for a specific domain to their HTTPS equivalent. This enhances user security by encrypting data.
This rule redirects any HTTP request for example.com to its HTTPS version.
[
{
"id": 2,
"priority": 1,
"action": {
"type": "redirect",
"redirect": {
"transform": {
"scheme": "https"
}
}
},
"condition": {
"urlFilter": "http://example.com/*",
"resourceTypes": ["main_frame", "sub_frame", "script", "image", "stylesheet"]
}
}
]Introducing `regexSubstitution`
Sometimes you don't want to redirect to a fixed URL, but rather modify parts of the original URL. This is where regexSubstitution comes in. It uses regular expressions to match and replace parts of the URL.
The matched parts from the regexFilter in the condition can be referenced in the substitution string using backreferences like \1, \2, etc.
Rewriting URL Paths Example
Imagine you have old URLs like /users/123 and want them to become /profile/123. You can use regexSubstitution to capture the ID and rewrite the path.
This rule captures the number after /users/ and reuses it in the /profile/ path.
[
{
"id": 3,
"priority": 1,
"action": {
"type": "redirect",
"redirect": {
"regexSubstitution": "https://www.example.com/profile/\\1"
}
},
"condition": {
"regexFilter": "^https://www.example.com/users/([0-9]+)$",
"resourceTypes": ["main_frame"]
}
}
]Modifying Query Parameters
regexSubstitution is great for cleaning up query parameters. You might want to remove a specific tracking parameter, like utm_source, from URLs to improve privacy or simplify sharing.
This rule matches URLs with ?utm_source=... and removes that parameter, keeping everything else.
[
{
"id": 4,
"priority": 1,
"action": {
"type": "redirect",
"redirect": {
"regexSubstitution": "\\1"
}
},
"condition": {
"regexFilter": "^(https?://[^?]+)\\?utm_source=[^&]*(?:&(.*))?$",
"resourceTypes": ["main_frame"],
"excludedInitiatorDomains": ["example.com"]
}
}
]Match Patterns & Regular Expressions
Remember, `urlFilter` uses match patterns, which are simpler for basic matches. `regexFilter` requires full regular expressions and is used when you need to capture parts of the URL for `regexSubstitution`.
- Match Patterns: Wildcards like
*, specific schemes/hosts. - Regular Expressions: Powerful pattern matching with groups
()and special characters.
Choose the right tool for the job!
Redirect Challenge
Consider a rule designed to redirect all requests from http://insecure.com to https://secure.com. Which `redirect` action type is best suited for this goal?
Recap: Redirects & Rewrites
Great job! You've learned how to powerfully control network requests:
- Redirects: Send requests to entirely new URLs using `redirect` with a `url`.
- Rewrites: Modify parts of URLs using `redirect` with `transform` or `regexSubstitution`.
- HTTPS enforcement: A practical use of `transform` to upgrade connections.
- URL cleaning: Use `regexSubstitution` to remove or change parameters.
These techniques allow you to enhance security, fix issues, and customize user browsing experiences.
Frequently asked questions
Is the “Redirecting & Rewriting URLs” lesson free?
Yes — the full text of “Redirecting & Rewriting URLs” is free to read here on the web, and the Browser Extensions Development (Chrome & Edge) course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Browser Extensions Development (Chrome & Edge) course, upgrade to CoddyKit PRO.
What will I learn in “Redirecting & Rewriting URLs”?
Discover how to redirect network requests to different URLs or rewrite parts of URLs based on defined criteria. You practise Browser Extensions Development (Chrome & Edge) with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start Browser Extensions Development (Chrome & Edge)?
No prior experience is required. Browser Extensions Development (Chrome & Edge) on CoddyKit is structured for beginners through advanced learners; this is — lesson 3 of 4, so you can start here or from the beginning and move at your own pace.
How long does the “Redirecting & Rewriting URLs” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this Browser Extensions Development (Chrome & Edge) lesson?
Yes. Every Browser Extensions Development (Chrome & Edge) lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Blocking Network Requests
- Modifying Request Headers
- Redirecting & Rewriting URLs
- Dynamic Rules & Debugging declarativeNetRequest