What is Let's Encrypt validation server?
The Let's Encrypt validation server is a bot that verifies domain ownership as part of the process for issuing free SSL/TLS certificates. This bot visits websites to complete domain validation challenges required before certificate issuance as part of their automated system. Agent Analytics can track when it visits your website.
Category
Expected Behavior
Let's Encrypt validation server's pattern depends on who pointed it at you. Continuous monitoring services check daily or even hourly, while a one time assessment sweeps once and disappears. Expect requests aimed at login pages, admin paths, APIs, and configuration files, because exposed ones are what scanners exist to find.
Overview
| Operated By | Let's Encrypt |
| Expected To Follow Robots.txt | Yes |
| Insights Last Updated | July 6, 2026 |
Robots.txt Blocked Percentage
Country of Origin
Robots.txt Blocking Trend
As of July 6, 2026, 0% of top websites block Let's Encrypt validation server in their robots.txt files.
Overall Security Scanner Traffic
As of July 6, 2026, 0.0% of all web traffic came from security scanners.
Top Visited Website Categories
This data reflects agent visits measured across thousands of websites using Agent Analytics, combined with daily scans of the world's top 1000 websites and their robots.txt files.
Let's Encrypt validation server's User Agent
| User Agent | Mozilla/5.0 (compatible; Let's Encrypt validation server; +https://www.letsencrypt.org) |
Access other known user agents and IP addresses using the Enterprise API.
How To Block Let's Encrypt validation server
Add this rule to your robots.txt file to block Let's Encrypt validation server from accessing your entire website. You can customize which pages are blocked by swapping out / for a different path.
User-agent: Let's Encrypt validation server # https://knownagents.com/agents/lets-encrypt-validation-server
Disallow: /Frequently Asked Questions
Should I Block Let's Encrypt validation server?
Not unless you already run your own scanning and want cleaner logs. Let's Encrypt validation server checks websites for exposed vulnerabilities, and some scanning services report what they find to site owners for free. Almost none of the top websites we track have robots.txt rules for Let's Encrypt validation server right now.
Does Let's Encrypt validation server Respect Robots.txt?
Yes. Let's Encrypt validation server is expected to honor robots.txt rules, so a disallow rule is the right first move. Automatic Robots.txt adds and maintains that rule for you, and Agent Analytics confirms Let's Encrypt validation server actually honors it.
Does Let's Encrypt validation server Access Private Content?
It probes for private content deliberately. Login pages, admin panels, and API endpoints are exactly what Let's Encrypt validation server tests, because exposed ones are what it exists to find. Probing is not the same as getting in, but expect requests to sensitive paths in your logs.
Why Is Let's Encrypt validation server Visiting My Website?
Let's Encrypt validation server is scanning your site for vulnerabilities, either as part of a sweep across the whole internet or because someone requested an assessment of your domain. Recurring visits usually mean a monitoring service has you on its list.
How Can I Tell if Let's Encrypt validation server Is Visiting My Website?
Agent Analytics tracks Let's Encrypt validation server visits in real time alongside every other known AI agent, crawler, and scraper. You can also check your server logs for requests whose user agent string contains "Let's Encrypt validation server". Look for probes of login, admin, and API paths. Keep in mind that Let's Encrypt validation server doesn't publish a verification method, so any client can claim its user agent string and a log match is a hint rather than proof.