Location
United States
Country level only
Domain
marcjenkins.co.uk
Served through Cloudflare's network, which answers from the location nearest each visitor.
Still looking this up. This tab fills in as the answers arrive.
Network Every network on the internet has an autonomous system number (ASN). This is the one that announces this address.
AS13335Cloudflare
Cloudflare, Inc.
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 valid104.21.80.0/20
Seen by 3,406 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
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
Tracing from a probe near you with Globalping. Hop locations that its round-trip times rule out are left off the map.
DNS records
TypeNameValueTTL
Amarcjenkins.co.uk104.21.95.155 min
Amarcjenkins.co.uk172.67.169.395 min
AAAAmarcjenkins.co.uk2606:4700:3033::6815:5f0f5 min
AAAAmarcjenkins.co.uk2606:4700:3033::ac43:a9275 min
NSmarcjenkins.co.uksuzanne.ns.cloudflare.com1 day
NSmarcjenkins.co.ukvicky.ns.cloudflare.com1 day
MXmarcjenkins.co.uk10 in1-smtp.messagingengine.com5 min
MXmarcjenkins.co.uk20 in2-smtp.messagingengine.com5 min
TXTmarcjenkins.co.uk"google-site-verification=ilOD4ELCQlwx3xoeClAit88a-O48VsT8ZJeD6KMW-p0"5 min
TXTmarcjenkins.co.uk"v=spf1 include:servers.mcsv.net ?all"5 min
TXTmarcjenkins.co.uk"v=spf1 include:spf.messagingengine.com ?all"5 min
HTTPSmarcjenkins.co.uk1 . alpn=h3,h2 ipv4hint=104.21.95.15,172.67.169.39 ech=AEX+DQBBuQAgACBJd9yXs07dlRnZ68LhTwNCPlph9bOtO6ibiePn44zcaAAEAAEAAQASY2xvdWRmbGFyZS1lY2guY29tAAA= ipv6hint=2606:4700:3033::6815:5f0f,2606:4700:3033::ac43:a9275 min
Partly protected
More than one SPF record, so receivers treat it as invalid.
- Receives mail
- Fastmail
- Mail servers
- in1-smtp.messagingengine.comin2-smtp.messagingengine.com
- SPFLists the servers allowed to send mail for the domain. Receivers check it against the sending server.
- Invalid0 of 10 DNS lookups
- DMARCTells receivers what to do with mail that fails SPF and DKIM: nothing (none), spam folder (quarantine) or reject.
- Missing
- 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).
- Not requested
- BIMIA brand logo that some mail apps show next to authenticated mail from the domain.
- Not published
Website
Page
Marc Jenkins
I am writing about my experiences as a self-employed web developer and designer.
- Language
- English
- Generator
- Eleventy v3.1.6
Built with
- CloudFrom the provider's published address ranges.
- Cloudflare
- CDN
- Cloudflarecf-ray header
- Framework
- Eleventygenerator tag “Eleventy v3.1.6”
Tech stack
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
Framework
- Eleventy3.1.6
generator tag “Eleventy v3.1.6”
Fonts
- Tiempos Text
self-hosted font
- Tiempos Headline
self-hosted font
- Suisseintl
self-hosted font
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.
- PrerenderedEleventy builds static HTML
- 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).
- Not cachedCloudflare
- Cache-Control
- public, max-age=0, must-revalidate
- HTML
- 5.8 KB
- Scripts
- 2 files1 from other sites · 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.
- Analytics
- Fathom
- Integrity checksSubresource Integrity: the script tag carries a hash of the file, so the browser refuses it if the other site changes it. Analytics and tag manager scripts change by design and can't carry one; pinned library files can.
- 0 of 1 script
AI & agents
Open to AI crawlers
robots.txt lets every AI crawler in.
Crawlers
Allows allTrainingSearchOn 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.
OpenAIGPTBotallowedOAI-SearchBotallowedChatGPT-Userallowed
AnthropicClaudeBotallowedClaude-SearchBotallowedClaude-Userallowed
GoogleGoogle-ExtendedallowedGooglebotallowed—
Microsoft—bingbotallowed—
AppleApplebot-ExtendedallowedApplebotallowed—
Perplexity—PerplexityBotallowedPerplexity-Userallowed
MetaMeta-ExternalAgentallowedMeta-WebIndexerallowedMeta-ExternalFetcherallowed
AmazonAmazonbotallowedAmzn-SearchBotallowedAmzn-Userallowed
MistralMistralAI-TrainingallowedMistralAI-IndexallowedMistralAI-Userallowed
OthersCCBotallowedBytespiderallowedDuckAssistBotallowed
- 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.
- ChatGPT searchClaudePerplexityAI OverviewsGeminiCopilotMeta AISiri
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.
- 214 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.
- Not published
- 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.
HTTPS
Certificate
Valid- Issuer
- Sectigo
- Issuing CA
- Sectigo Public Server Authentication CA DV E36
- Covers
- *.marcjenkins.co.uk, marcjenkins.co.uk
- Also validOther unexpired certificates for this name, found in Certificate Transparency logs.
- 7 more certificates
Sep 17, 202658 days leftDec 9, 2026
From Certificate Transparency logs, via Cert Spotter.
Security
F- HSTSStrict-Transport-Security makes browsers refuse plain HTTP to this site. Preloaded sites are HTTPS-only even on a first visit.
- Not sent
- HTTP → HTTPSWhether the plain http:// address redirects visitors to the secure one.
- Redirects
- HTTP/3The newest HTTP, over QUIC. Announced in the alt-svc header or the domain's HTTPS DNS record.
- Available
- Encrypted helloEncrypted Client Hello (ECH) hides which site you're visiting from anyone watching the connection.
- Supported
- CAADNS records naming the only certificate authorities allowed to issue certificates for the domain.
- Any CA may issue
- security.txtA standard file (RFC 9116) telling security researchers how to report vulnerabilities.
- Not published
Security headers 2 of 7
- HSTSmissing
- CSPmissing
- Framingmissing
- No sniffingpresent
- Referrerpresent
- Permissionsmissing
- Isolationmissing
Response
200 OK125 ms from CMHDNS lookup24 ms
200 marcjenkins.co.uk125 ms
DNSConnect (TCP + TLS)Waiting for the replyFrom Cloudflare's CMH data center
Response headers
- access-control-allow-origin
- *
- cache-control
- public, max-age=0, must-revalidate
- cf-cache-status
- DYNAMIC
- cf-ray
- a497ce0cad07a691-CMH
- connection
- close
- content-type
- text/html; charset=utf-8
- date
- Mon, 12 Oct 2026 17:25:37 GMT
- nel
- {"report_to":"cf-nel","success_fraction":0.0,"max_age":604800}
- referrer-policy
- strict-origin-when-cross-origin
- report-to
{"group":"cf-nel","max_age":604800,"endpoints":[{"url":"https://a.nel.cloudflare.com/report/v4?s=Ul1hRDzhEvWFhJ7pTFJwzqbOXacz7Sueq1feS%2FrecSTlM9Ip7xHgbI%2BKohUBIkbTJgpqJVvJqwLz4pJdRbNdwRegtBE0oP%2FByQnNTeXgy2eLvb%2FQ9OkGnrp4eTLy%2B%2Bh32X2… Show all
{"group":"cf-nel","max_age":604800,"endpoints":[{"url":"https://a.nel.cloudflare.com/report/v4?s=Ul1hRDzhEvWFhJ7pTFJwzqbOXacz7Sueq1feS%2FrecSTlM9Ip7xHgbI%2BKohUBIkbTJgpqJVvJqwLz4pJdRbNdwRegtBE0oP%2FByQnNTeXgy2eLvb%2FQ9OkGnrp4eTLy%2B%2Bh32X2Fg6sAB1nXrxgYv3dgvg%3D%3D"}]}- server
- cloudflare
- transfer-encoding
- chunked
- x-content-type-options
- nosniff
Details
Network
- IPv4
- 104.21.95.15
- ASNThe autonomous system number of the network that announces this address.
- AS13335
- Operator
- Cloudflare, Inc.
- CDNFrom the provider's own published list of its address ranges.
- Cloudflare
- PrefixThe block of addresses announced over BGP that contains this address.
- 104.21.80.0/20
- RPKIWhether a signed record (ROA) authorizes this network to announce this prefix.
- Valid
- VisibilityHow many bgp.tools peers carry this announcement.
- 3,406 peers
- Type
- Content
- Registry
- ARIN
Location
Country level- Country
- United States
- Continent
- North America
Registration
RDAP- Registrar
- Krystal Hosting Ltd
- Registered
- Apr 26, 200719 years ago
- Expires
- Apr 26, 2028next year
- Updated
- Feb 13, 2026
- StatusRegistry flags on the domain, such as locks that stop unauthorized transfers or changes.
- Active
- DNSSECDNSSEC signs DNS answers so they can't be forged on the way to you.
- Unsigned
- Name servers
- suzanne.ns.cloudflare.com.vicky.ns.cloudflare.com.
- Registrant
- Redacted for privacy
Apr 26, 2007562 days leftApr 26, 2028