01 · Operator
Who operates Jigsaw
- Company
- W3C
- Type
- Other bot
- Official docs
- jigsaw.w3.org
02 · Behavior
What Jigsaw does
The W3C CSS Validator checks style sheets and HTML documents against the CSS specifications. It reports errors, typos and incorrect CSS. Requests come when someone validates a page or style sheet by URL.
03 · Impact
Why Jigsaw matters for your site
If you allow it
- Lets you and others validate your CSS
- Low request volume
If you block it
- No search visibility
- Can be run by anyone against your site
04 · Allow
How to allow Jigsaw
robots.txt
User-agent: Jigsaw
Allow: /Cloudflare
# Security › WAF › Custom rules › Create rule
Expression: (http.user_agent contains "Jigsaw")
Action: Skip › All Super Bot Fight Mode rules
# Also check Security › Bots: "Block AI bots" can block it regardless of robots.txt.WordPress
# WordPress serves a virtual robots.txt. Edit it with your SEO plugin:
# Yoast: SEO › Tools › File editor · Rank Math: General Settings › Edit robots.txt
User-agent: Jigsaw
Allow: /nginx
# nginx serves every user agent by default.
# Make sure no rule like this blocks it:
# if ($http_user_agent ~* "Jigsaw") { return 403; }Apache
# Apache serves every user agent by default.
# Make sure .htaccess has no rule like this:
# RewriteCond %{HTTP_USER_AGENT} Jigsaw [NC]
# RewriteRule .* - [F,L]05 · Block
How to block Jigsaw
Start with robots.txt. If Jigsaw keeps showing up in your logs, block it at your CDN or web server.
robots.txt
User-agent: Jigsaw
Disallow: /Cloudflare
# Security › WAF › Custom rules › Create rule
Expression: (http.user_agent contains "Jigsaw")
Action: BlockWordPress
# WordPress serves a virtual robots.txt. Edit it with your SEO plugin:
# Yoast: SEO › Tools › File editor · Rank Math: General Settings › Edit robots.txt
User-agent: Jigsaw
Disallow: /nginx
# In your server { } block:
if ($http_user_agent ~* "Jigsaw") {
return 403;
}Apache
# .htaccess
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteCond %{HTTP_USER_AGENT} Jigsaw [NC]
RewriteRule .* - [F,L]
</IfModule>06 · User agents
User agents we see for Jigsaw
The operator does not publish a full user agent string. Requests contain the token “Jigsaw”.
07 · Verification
Is it really Jigsaw?
Jigsaw’s operator publishes no IP ranges or hostnames, so requests cannot be verified. Treat the user agent as a claim, and watch your logs for unusual request rates.
FAQ
Questions about Jigsaw
What is Jigsaw in my server logs?
It is the W3C CSS Validator, which W3C hosts at jigsaw.w3.org. It fetches pages or style sheets that a user submits for validation.
Is the Jigsaw user agent a crawler?
It is a validation tool, not a search crawler. Its About page does not describe automatic crawling.
Last reviewed Oct 8, 2026