BGP prefixPrefix
The block of addresses this IP is announced in to the rest of the internet. RPKI valid means the block's owner
signed off on the network announcing it.
RPKI valid
104.26.0.0/20
Seen by 3,405 peers
Latency
Round trip for an HTTPS request from your browser to the site and back, including the server's reply time.
Live
— ms
Measuring from your browser…
At a glance
Route
From Columbus on Anthropic, PBC
YouColumbus
Finding a probe near you…
Networks crossed
Each network is an autonomous system (AS). Your traffic is handed from one to the next where they connect, following
the routes BGP advertises.
AS16509Anthropic, PBC
AS13335Cloudflare
#HostNetworkLocationRound trip
AS
⋮
Waiting for a reply——*
Tracing from a probe near you with Globalping. Hop locations that its round-trip times rule out are left off the map.
Email
Protected from spoofing
Mail that fails its checks is sent to spam under getground.co.uk's DMARC policy, so forged mail doesn't reach inboxes.
Receives mail
Google Workspace
Mail servers
aspmx.l.google.comalt1.aspmx.l.google.comalt2.aspmx.l.google.com+2 more
SPFLists the servers allowed to send mail for the domain. Receivers check it against the sending server.
Rejects everything else4 of 10 DNS lookups · includes _spf.google.com, sendgrid.net…
DMARCTells receivers what to do with mail that fails SPF and DKIM: nothing (none), spam folder (quarantine) or reject.
Quarantinesends reports
MTA-STSRequires other mail servers to use encrypted connections (TLS) when delivering to this domain.
Not published
TLS reportsAsks other mail servers to report failed encrypted deliveries (TLS-RPT).
Requested
BIMIA brand logo that some mail apps show next to authenticated mail from the domain.
Built with
Each entry says what gave it away: a response header, a cookie's name, an asset's path or file name, or markup the tool leaves in the page.
Versions are checked against endoflife.date's support schedules and, for JavaScript packages, OSV's vulnerability database, which carries
GitHub's security advisories.
CDN & edge
Cloudflare
cf-ray header
Fonts
DM Sans
from Google Fonts
Doto
from Google Fonts
Inter
from Google Fonts
Rethink Sans
from Google Fonts
IBM Plex Serif
from Google Fonts
How it's made
RenderingPrerendered pages are built ahead of time and served as files. Pages rendered on each request are built by server code for every visitor. Pages drawn in the browser arrive nearly empty and depend on JavaScript, which most AI crawlers don't run. Islands are interactive parts in otherwise static HTML.
Drawn in the browseralmost no text (0 words) until scripts run
Edge cacheWhether a CDN or proxy answered heade.rs's request from its cache, and how long ago that copy was made (the Age header).
Served from cacheCloudflare
Cache-Control
public, max-age=0, must-revalidate
HTML
19.9 KB
Scripts
1 file · 7 inlineall from this site · 1 modules
Code from other sites
Scripts a page loads from another domain run with the same power as its own code: they can read what visitors type and change the page.
heade.rs checks what the HTML loads, not what tag managers add once they run.
The front page shows almost no text until scripts run (0 words), and GPTBot, ClaudeBot and PerplexityBot don't run them.
Crawlers
Allows all
TrainingSearchOn request
They visit a page when someone asks an assistant about it. ChatGPT's, Perplexity's, Meta's and Amazon's treat robots.txt as advisory;
Anthropic's and Mistral's follow it.
Can cite itThe AI products that can use the site in their answers: each answers from one crawler (OAI-SearchBot for ChatGPT search, Googlebot for AI Overviews, bingbot for Copilot), and robots directives on the front page, like noindex, nosnippet and noarchive, keep some out.
It's on Cloudflare, which can also block AI crawlers at its edge whatever robots.txt says.
Reading
Without JavaScriptText on the front page before any scripts run: what GPTBot, ClaudeBot, PerplexityBot and most agents read. Google, Bing and Apple's crawlers run scripts.
Almost no text0 words
MarkdownAgents like Claude Code, Cursor and OpenCode ask for Markdown in their Accept header. It's the page without its markup, so it costs them far fewer tokens.
Not offered
llms.txtA Markdown file listing a site's key pages for AI tools. Coding agents read it; search crawlers mostly don't.
Structured dataschema.org JSON-LD in the page: facts about the site in a form machines read directly.
None on the front page
Tools
Ways an AI agent can do things on the site, not just read it: an MCP server that apps like Claude, ChatGPT and Cursor connect to, an API
catalog, packaged agent skills, a shopping profile (UCP), or tools the page offers AI in the browser (WebMCP). heade.rs looks in the official
MCP Registry and the files the site publishes under /.well-known/.
No MCP server, API catalog, agent skills, shopping profile or in-page tools found.