jeroenjanssens.com

.com crawl

First seen 2026-04-13 · Last seen 2026-05-08 · ok HTTP/1.1 200 645 ms crawled 2026-05-07

US · 188.114.97.3 · AS13335 Cloudflare, Inc.

Reputation 87/100 weak security headers no dmarc policy

Classifying

HTML metadata

Title

Jeroen Janssens

Description

📛 I'm Jeroen (pronounced Yuh-ROON). Welcome to my site. 💻 I work at Posit, PBC as Head of Developer Relations. ✍️ Together with Thijs Nieuwdorp I wrote Python Polars: The Definitive Guide. I’m also the author of Data Science at the Command Line. 🐛 Most of my bugs are written in Python, R, JavaScript and Bash. Every now and then I dabble in C and Lua. I should learn Rust. 🇳🇱 I live in Rotterdam, the Netherlands with my wife and two kids. 🗽 My wife and I have lived in New York City for 2,5...

Language

Feeds

Atom Atom

Open Graph

title: Jeroen Janssens
locale: en
site name: Jeroen Janssens
description: 📛 I'm Jeroen (pronounced Yuh-ROON). Welcome to my site. 💻 I work at Posit, PBC as Head of Developer Relations. ✍️ Together with Thijs Nieuwdorp I wrote Python Polars: The Definitive Guide. I’m also the author of Data Science at the Command Line. 🐛 Most of my bugs are written in Python, R, JavaScript and Bash. Every now and then I dabble in C and Lua. I should learn Rust. 🇳🇱 I live in Rotterdam, the Netherlands with my wife and two kids. 🗽 My wife and I have lived in New York City for 2,5...

Technology

CDN: Cloudflare
CMS: Gatsby

Analytics

Cloudflare Insights

Social widgets

YouTube Embed

Third-party hosts loaded (3)

www.youtube.com×3
static.cloudflareinsights.com×2
f.convertkit.com×1

Social

Registration

Registrar

Realtime Register B.V.

Created

2005-05-04

Expires

2027-05-04 348 days left

Updated

2026-05-05

Name servers

roxy.ns.cloudflare.com
yahir.ns.cloudflare.com

DNS records live

NS

roxy.ns.cloudflare.com
yahir.ns.cloudflare.com

MX

1 aspmx.l.google.com
10 alt3.aspmx.l.google.com
10 alt4.aspmx.l.google.com
5 alt1.aspmx.l.google.com
5 alt2.aspmx.l.google.com

Verified for

Google

Email authentication partial

SPF: not published
DMARC: not published
DKIM: no key found at common selectors

Certificate (current)

WE1

from 2026-05-02 to 2026-07-31

Expires in 71 days

Full certificate history on crt.sh ↗

HTTP security headers

Header hygiene 45/100 Checked live page: https://jeroenjanssens.com/

present

x-content-type-options
referrer-policy

findings

missing HSTS
missing Content Security Policy
missing frame protection
missing Permissions Policy

Header values

referrer-policy: strict-origin-when-cross-origin
x-content-type-options: nosniff