Robots.txt Guide: How It Works, Best Practices & SEO Impact

Robots.txt is a simple text file that instructs web crawlers on how to crawl a website and is an important aspect of Search Engine Optimization (SEO). A site owner uses `robots.txt` to effectively guide search engines regarding pages not to be indexed. By doing this, a site owner brings Search Engine Optimization activities under control and prevents the crawling, and indexing of duplicate content and sensitive content.

History of `robots.txt`

The Robots Exclusion Protocol, or robots.txt, was invented in 1994 with the idea of providing standard ways for webmasters & crawlers to communicate with one another. Eventually, the standard was taken into account by major search engines such as Google, Bing, and Yahoo!.

How `robots.txt` Works

The `robots.txt` file must be placed in the root directory of a website. For example, it should be accessible at `https://www.example.com/robots.txt`.

It only takes a few steps to see how `robots.txt` works. Let's take a look:

Step 1: Crawlers Request Access

1. Start: When a web crawler (such as Googlebot) visits a website, it requests access to the `robots.txt` file first.
2. URL Request: The crawler requests access to the file, i.e., by accessing `https://www.example.com/robots.txt`.

Step 2: Server Response

1. File Retrieved: If the file exists, the web server responds with the content of the `robots.txt` file.
2. 404 Error Handling: If the file does not exist, then the web server will return a 404 error, and the crawler has access to all content by default.

Step 3: Parsing the Directives

1. Read File: The crawler will read the directives in the `robots.txt` file. The crawler sees which user-agents (crawlers) the rules apply to and which directories or pages are disallowed or allowed.

Step 4: Following the Rules

The crawler decides based on the directives:

1. If the path is  Disallowed - the crawler will not index or access this path.
2. If the path is Allowed - the crawler can index the content of that directory or page.  

Step 5: Indexing Content

1. Allowed Crawling: The crawler will crawl the allowed pages and once again collect the data needed to present in the search results.
2. Disallowed Crawling: The crawler ignores disallowed directories/pages, so it does not index them. 

Step 6: Maintenance

1. File Updates: The webmaster may update the `robots.txt` file whenever she/he/they chooses to specify parameters for crawler access.
2. Crawlers Revisit: Crawlers will periodically check the `robots.txt` file to determine whether the directives have changed.

How to locate the `robots.txt` File

Finding the `robots.txt` file for any website is very easy. Just follow these simple steps:

1. Open Your Web Browser: Launch any web browser such as Chrome, Firefox, or Safari.

2. Type the Website URL: In the address bar, type in the full URL of the website you want to check. For example, `https://www.example.com`.

3. Add `/robots.txt`: Once you've entered the website URL, add `/robots.txt`at the end of the URL. So now we'd enter `https://www.example.com/robots.txt`.

4. Press Enter: Once you've entered the URL, just press Enter and be taken to that specified URL.

5. View the File: If the website has a `robots.txt` file, it will appear. It will be in plain text. You can now see the directives that the website has put down in the file.

How to write & Submit the `robots.txt` File

A `robots.txt` file only needs a few steps to create and submit the file. Here is what you need to do:

Step 1: Create the `robots.txt` file

1. Open a Plain Text Editor: There are many plain text editors you can use, including Notepad (Windows), TextEdit (as a plain text file) (Mac), or you could use a code editor like VS Code.

2. Write your directives. Start by writing your `robots.txt` file in the proper syntax. Here are a few examples:

User-agent: *

Disallow: /private/
Allow: /public/

Sitemap: https://www.example.com/sitemap.xml

3. Save the File: Save the file as `robots.txt`. Make sure to save it using plain text format (not in Word or any other format).

Step 2: Upload the `robots.txt` File

1. Find Your Website's Root Directory: Use an FTP client (for example FileZilla) or your web hosting's control panel (for example cPanel) to access the files for your website.

2. Go to the Root Directory: This is usually the folder where your website files are located, with the folder title being `public_html` or similar.

3. Upload the File: Drag and drop the `robots.txt` file into the root directory. Make sure it's at the top level and not in one of the subfolders.

Step 3: Verify the `robots.txt` File

1. Open Your Web Browser: You will need to open any web browser.

2. Enter the URL: Write your website url and add `/robots.txt` to the end (for example: `https://www.example.com/robots.txt`)

3. Check That It Displays Correctly: Make sure that the file displays and follows the directives that you wrote.

Step 4: Validate the `robots.txt` File

1. Google Search Console:

   - Log in to your Google Search Console account.

   - Pick the website property you want to work with.

   - Go to "Settings" > "Crawling" > "robots.txt".

   - After this, click on open report to test your `robots.txt` file.

2. Bing Webmaster Tools:

   - Log in to Bing Webmaster Tools

   - Select Your Website Property

   - Click on “Tools & Enhancements”>“robots.txt Tester”

   - Validate Your robots.txt File

Step 5: Monitor and Update

- Regular Check: Perform an occasional check of your `robots.txt` file to make sure it reflects your current needs. 

- Update as Needed: If you change your website structure or content, make changes in the `robots.txt` file as needed and re-upload it.

Example Structure:

User-agent: *

Disallow: /private/

User-agent: the crawler being specified.

Disallow: Indicates which paths should not be accessed.

Common Directives in `robots.txt`

Robots.txt Best Practices:

1. Keep it Simple: Your rules should be clear and unambiguous. Do not use complicated conditions.
2. Ensure Accessibility for Important Content: Be careful to allow access to the pages that are important to you.
3. Test the File: You can use tools such as Google Search Console to check for errors.
4. Update Regularly: Review the file regularly as your site changes over time.

Common Mistakes to Avoid

Testing Ensuring robots.txt is functional 

- Google Search Console (use for robots.txt validation) 

- web server logs (check bots that visited the blocked address)

- Robots.txt checkers (have some online options). 

Example 

Case Studies:

1. Amazon.com 

- Use robots.txt to block specific paths to optimize crawling, e.g.

    User-agent: *

    Disallow: /gp/cart

2. YouTube:

   - Disallows user-specific pages to protect privacy.

   - Example:

     user-agent: *

     Disallow: /login

Advanced Topics

1. Dynamic Generation: Some sites may generate `robots.txt` based on user sessions or as content is updated.
2. As Part of your SEO Strategy: Use the `robots.txt` file in conjunction with the use of meta tags as well as canonical links to optimize for SEO.
3. Performance considerations: A well-designed `robots.txt` can potentially increase your site speed by reducing the load on the server for disallowed files.

Conclusion

In summary, `robots.txt' is a valuable resource for webmasters to achieve some control of how web crawlers behave. Webmasters who check and frequently update the `robots.txt' file will help enhance the SEO of their websites. As a webmaster, such a basic understanding of the structure and directive values in 'robots.txt' files is essential.