33 corners of the internet worth bookmarking this week, from a DNS propagation checker to a site where you bounce cats.
Scans known data breaches for your email address and tells you which ones leaked it, with concrete steps to lock down each account. No sign-up needed to run a scan.
Generates single-use or merchant-locked virtual card numbers so a sketchy checkout page never touches your real card. US-only, but the free tier covers most everyday shopping.
Spins up a disposable inbox in seconds for sign-up forms you don't trust. Messages self-destruct after an hour, and you can reply from the address if you need to.
Routes your query through Google, strips out every tracker and cookie, and hands you back Google-quality results without building a profile on you in the process.
Michael Bazzell's free OSINT tool index: hundreds of hand-picked lookup tools sorted by category (usernames, phone numbers, images) instead of one search box claiming to do everything.
Tracks growth history for YouTube, Twitch, TikTok, and Instagram accounts going back years, useful for spotting a fake follower spike or sizing up a channel before a sponsorship deal.
Pulls a page's cached or archived version from the Wayback Machine, archive.today, and a couple of other sources in one search. Handy when a site goes down or quietly edits a page.
Runs weekly scans across the entire internet and lets you search the results, an alternative to Shodan and Censys with its own dataset of exposed devices and services.
Hosts intentionally broken virtual machines you download and try to break into yourself, a hands-on alternative to reading about penetration testing instead of doing it.
Flips the CTF format around: instead of breaking into systems, you work incident-response scenarios and forensic evidence like an actual SOC analyst on shift.
OffSec's searchable archive of public exploits and proof-of-concept code, the reference researchers pull up to check whether a CVE actually has working exploit code attached.
A crowdsourced blacklist where sysadmins report IPs caught spamming, scanning, or brute-forcing logins, so you can check an address's rap sheet before deciding to block it.
Rewrites man pages as short, example-driven cheat sheets. Type tldr tar and get five commands people actually use instead of a wall of flags nobody memorizes.
Runs your site through real browsers on real devices from 40 locations and returns a waterfall chart of exactly what loaded slowly and why. Open-source and free, where several rivals now paywall the useful parts.
Checks a DNS record against resolvers in 20-plus countries at once, so after you change a record you can watch how far the update has actually spread instead of guessing and refreshing.
An AI search layer that cites its sources inline and switches between chat, code, and image modes without ever leaving the results page.
Free chat interface for open-source models, currently routing across more than a hundred of them, with an auto mode that picks whichever model actually fits your question.
Type a genre and a lyric idea, get back a full song with vocals in under a minute, a different flavor of AI music generation than the more famous name in this space.
Upload a spreadsheet, ask questions about it in plain English, and it writes and runs the analysis code itself, then hands back a chart instead of a formula you'd have to build.
Edits video and audio by editing the transcript: delete a sentence in the text and the matching clip disappears with it. The free plan covers recording, editing, and export.
Turns a text prompt or still photo into a short, physically plausible video clip in under a minute. Free generations are watermarked; clean exports start at $30 a month.
No-frills image host: drop a file in, get a direct link and BBCode back immediately, no account required for a quick upload.
Free diagramming tool for flowcharts, ER diagrams, and network maps that imports files straight from Visio or Lucidchart if you're trying to leave either one behind.
Look up any CSS or HTML feature and see exactly which browser versions support it, the tab every front-end developer keeps open somewhere in the background.
Write an OpenAPI spec on the left, watch the rendered API docs update live on the right, and catch formatting mistakes before they reach your real documentation.
Over a thousand pages of investing reference written and maintained by an online community built around low-cost index investing. No ads, no affiliate links, no login wall.
Backtests any asset allocation against 56 years of market data and shows the worst-case drawdown, not just the rosy average return everyone likes to quote.
An open-ended text adventure where an AI improvises the story around whatever you type next. No two playthroughs land the same way.
Multiplayer tank arena where you grind shapes for XP and pick an upgrade path at every level, from the creator of Agar.io.
Caltech's free, fully rebuilt online edition of Feynman's original physics lectures, with equations and figures that stay sharp at any zoom instead of a scanned PDF.
A nonprofit library of free, editable college textbooks across 17 subjects, built so professors can remix chapters instead of assigning a $300 book.
Walks you through a short sequence of low-effort yes/no questions about water, food, and sleep to figure out what's actually wrong when you can't tell yourself.
Click and the cats bounce. That's the entire site, and it's somehow still satisfying more than fifteen years in.