Trailing slash normalization in Nginx - Step-by-Step Execution

Process Flow - Trailing slash normalization

Request URL Received

↓

Check if URL ends with '/'

↓

Final Response Sent

The server checks if the requested URL ends with a slash. If yes, it redirects to the same URL without the trailing slash using a 301 redirect. Otherwise, it serves the URL as is.

Execution Sample

Nginx

location / {
  if ($request_uri ~ "^(.+)/$") {
    return 301 $scheme://$host$1;
  }
}

This nginx config redirects URLs ending with a trailing slash to the same URL without it.

Process Table

Step	Request URL	Condition ($request_uri ~ "^(.+)/$")	Action	Resulting URL	Response
1	/about/	True	Redirect to URL without trailing slash	/about	301 Moved Permanently
2	/about	False	Serve URL as is	/about	200 OK
3	/contact/	True	Redirect to URL without trailing slash	/contact	301 Moved Permanently
4	/contact	False	Serve URL as is	/contact	200 OK
5	/	False	Serve URL as is	/	200 OK

💡 Requests without trailing slash are served directly; requests with trailing slash are redirected once.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
$request_uri	/about/	/about/	/about	/contact/	/contact	/
Condition Result	N/A	True	False	True	False	False
Resulting URL	N/A	/about	/about	/contact	/contact	/
Response	N/A	301	200	301	200	200

Key Moments - 3 Insights

Why does the server redirect when the URL ends with a slash?

Because the condition ($request_uri ~ "^(.+)/$") matches URLs ending with a slash, triggering a 301 redirect to the URL without the trailing slash as shown in steps 1 and 3 of the execution_table.

What happens if the URL is just '/'?

The condition is false for '/', so the server serves the URL as is with a 200 OK response, as shown in step 5 of the execution_table.

Does the server redirect URLs without trailing slashes?

No, URLs without trailing slashes do not match the condition and are served directly with 200 OK, as shown in steps 2 and 4.

Visual Quiz - 3 Questions

Look at the execution_table, what is the response code at step 3 for the URL '/contact/'?

A 301 Moved Permanently

B 200 OK

C 404 Not Found

D 500 Internal Server Error

💡 Hint

Check the 'Response' column in row 3 of the execution_table.

At which step does the condition ($request_uri ~ "^(.+)/$") evaluate to false for the first time?

A Step 1

B Step 3

C Step 2

D Step 5

💡 Hint

Look at the 'Condition' column in the execution_table rows.

If the URL '/blog/' is requested, what would be the resulting URL after redirection?

A /blog/

B /blog

C /blog/index.html

D /blog//

💡 Hint

Refer to how URLs ending with '/' are redirected in the execution_table steps 1 and 3.

Concept Snapshot

Trailing slash normalization in nginx:
- Check if URL ends with '/'
- If yes, redirect (301) to URL without trailing slash
- If no, serve URL as is
- Uses regex condition: $request_uri ~ "^(.+)/$"
- Helps avoid duplicate content and broken links

Full Transcript

Trailing slash normalization in nginx means the server looks at the requested URL. If the URL ends with a slash, the server sends a 301 redirect to the same URL without the slash. If the URL does not end with a slash, the server serves the page directly. This is done using a simple if condition with a regex that checks for a trailing slash. For example, '/about/' redirects to '/about' with a 301 status. URLs like '/' or '/contact' are served as is with a 200 status. This helps keep URLs consistent and avoids duplicate content issues.