Writing tests is hard, and I'm lazy. I'd rather write a few invariants, and let fast-check fuzz test the rest. That's why I built @​traversable/valibot-test. Here it is in action:

✨ We’re thrilled to welcome our new Gold Sponsor: LambdaTest! 🎉 Your support helps us keep improving fast-check for the whole community 💛 More about them at www.lambdatest.com

We are part of the trusted list 🚀

And here is the associated release note: fast-check.dev/blog/2025/09...

We also recently moved @fast-check.dev and all associated packages to Trusted Publishing to ensure a safer publication flow 🤗

New version of fast-check released 🚀

Did you know that @rolldown.rs supports converting your top-level variables to var? It seems weird at first, but is actually helpful - and your output is still ESM and modern code! The transform can improve perf due to avoiding "temporal dead zone" checks of VMs that can cause slowdowns up to 1000%

And finally the release note for the version 4.2.0 🤩 fast-check.dev/blog/2025/07...

🚀 fast-check 4.2.0 just got released It offers some new helpers to deal with race condition detection.

🍿 @fast-check.dev just got leveraged by our community to uncover two prototype pollutions in #Zod 🔐 Let's make the ecosystem safer with property based testing 🤗

🖼️ Lately we breached several months in a row the quotas of Git LFS on GitHub. It totally blocked our CI until we paid for extra quotas. Yesterday, we dropped Git LFS from our repository and outsourced heavy assets to another repository that we could fetch from when needed (bundling of the blog).

🎁 Fresh new version of fast-check is out! Mostly playing around race-conditions for this first minor of the 4.x series. This minor should make our scheduling primitives even more reliable and even more powerful. fast-check.dev/blog/2025/04...

🤫 Our proposal for flaky tests 🎲 Random failures can be a nightmare to debug. What if your test runner could control randomness natively—making tests more reliable & reproducible? Let discover our proposal to bring built-in fuzzing for free to @vitest.dev! 🔥 fast-check.dev/blog/2025/03...

Our latest version of the @fast-check/vitest plugin has just been released and it supports this syntax natively 🚀 Stop relying on indeterministic values in your @vitest.dev tests 🤗 More to come soon with a dedicated article on it ✍️

Already 1 week since the release and so far so good 🤞

✅ Bag and stickers packed for tonight 🤗 Looking forward to seeing many at the event of tonight and at React Paris

⏰ Counting days before Node 18 reaches EOL. Once reached the plan is to drop CJS from our published package 📦

🍿 Waiting for Node 18 to be EOL so that we can release a new major without CJS builds

@fast-check.dev is on "This Week In React 225" 🤩

Super excited to check this out🔥 Generating good default values from a schema is closely linked to having a fully reduced representation, which is one of my favorite problems in the world.

🚀 Version 4.0.0 is out! More details at fast-check.dev/blog/2025/03...

Three weeks ago @sxzz.dev updated Vitest to (mostly) adopt TypeScript's stricter Isolated Declarations mode 🎉 github.com/vitest-dev/v... This allowed @hiogawa.bsky.social to make Vitest use Oxc for DTS generation. Build time reduced from 90s to 27s - a 70% reduction 🔥 github.com/vitest-dev/v...

🍳 Cooking a few things for the next major of fast-check... More to come soon but it should arrive in the coming days 🤩

A glimpse at what’s coming to Effect Days: ◆ AI Agents ◆ Error Management & Testing ◆ Effect Cluster & Fibers ◆ Next-Gen DevTools ◆ Rebuilding Redis for great Effect ...and much more! 🎟️ Get your ticket now: effect.website/events/effec...

We recently moved from Yarn berry in PNP mode to @pnpm.io. So far so good, the CI performance is great and the switch has been smooth 👌

New blog post: the monad tutorial of my dreams, and maybe of yours! A jargon-free, practical explanation of monads as a design pattern, using Rust and property-based testing as the vehicle

Our next major is coming soon ☺️ Just piling the last few PRs and ensuring all needed breaking changes related to issues have been included 🚢 So far we have already released a new version of our random library: pure-rand 🎲

Oracle justified its JavaScript trademark by claiming Node.js — now it wants that ignored #FreeJavaScript deno.com/blog/deno-v-...

Fresh new release of @fast-check/vitest our integration of @fast-check.dev with @vitest.dev We officially support the version 3 of Vitest 🎉

He’s also the creator and maintainer of @fast-check.dev, the most popular #JavaScript fuzzing library with over 7M downloads per month.

Got a pretty extensive list of things to finish, one of them is to keep iterating on testing & benchmarks. I want to complement @bun.sh test with @fast-check.dev, so I can get a better framework to benchmark against Math.sin(), Math.cos().

I published my first Egghead video 😁 egghead.io/write-a-prop...

write durable tests with property-based testing using @fast-check.dev

Just received the first of a recurring sponsorship from @sentry.io ♥️

Explore the GitHub Sponsors pages of the maintainers of your favorite OSS projects. Find an awesome folk who deserves more support, then press the sponsor button to show them we appreciate their work. Today is a good day to give back.

🤫 Just started to merge the first PRs for the next major of fast-check. This time release is really soon 😅

Happy New Year 🎆

🎄 The final challenge is here! 🎅 Santa’s coin distribution for the elves is at risk. Can you help Emma ensure every elf gets paid fairly and efficiently using property-based testing? 🪙 It’s the last puzzle! 👉 fast-check.dev/blog/2024/12...

Advent of PBT · Day 23 🎄💰 Santa's payment delays pushed the elf Emma to create a coin-payment algorithm — but it might have bugs. After your impressive job, she decided to call you back. Can you test it to ensure elves get paid on time? 🔍 👉 fast-check.dev/blog/2024/12...

🔔 Advent of PBT 2024 · Day 22 🔔 Santa remastered a classic game with a festive twist: SantaMind! 🎄🎁 But there's a problem—his elves' feedback algorithm might have bugs! Can you find it to ensure every guess gets the right response? 🎅🐛 👉 fast-check.dev/blog/2024/12...

🎁🎮 Advent of PBT · Day 21 is here! Santa’s remastered Tic-Tac-Toe game adds a twist: a feature to check if you can still win! But can you be sure it’s bug-free? Use fast-check to uncover flaws and ensure every move matters! 👉 fast-check.dev/blog/2024/12...

🚨 Advent of PBT 2024 · Day 20 🚨 Santa tackled a coding puzzle to boost his morale but fears there might be a bug in his optimized solution. Can you prove him right (or wrong)? 🔍 Test his algorithm with fast-check and restore his confidence! 🎄✨ 👉 fast-check.dev/blog/2024/12...

🎄 Day 19 of the Advent of PBT is here! Santa’s sleigh-packing algorithm needs to be checked! Can you find a bug in the elves’ plan and ensure Santa minimizes his trips? The fewer trips, the faster the gifts! 🛷✨ Put your property-based testing skills to the test! 👉 fast-check.dev/blog/2024/12...

🎅✨ Advent of PBT 2024 · Day 18 ✨🎅 Santa’s journey-planning algorithm is live, but can it truly optimize his route? This year, every kilometer counts, and potential delays could risk Christmas! Ensure Santa’s path is optimal 🏠➡️🎁 👉 Dive into today’s puzzle: fast-check.dev/blog/2024/12...

🎄 Day 17: Email Validator Gone Rogue! 📧 Santa’s elves implemented a regex to secure his newsletter sign-ups, but Santa’s worried it might reject valid emails. Your challenge: find a valid email the regex flags as invalid. Christmas depends on you! 🛠️✨ 👉 fast-check.dev/blog/2024/12...

🎄 Day 16: Debugging Santa Codes! 🎅 Santa’s new counting system ensures every number differs by exactly one bit. Ingenious—but are the elves' algorithms bug-free? 🛠️ Can you find an input that breaks their "flawless" implementation? Christmas is in your hands! ✨ 👉 fast-check.dev/blog/2024/12...

Solved Advent of PBT 2024 day 1 with @fast-check.dev and @vitest.dev! 🎉 Property-based testing has been on my bucket list forever & it's so cool to learn it in the advent format. Inspiring!!! Also learned there's a Zod adapter--gonna try that next. 🤓

🎄 Day 15: Santa’s Shelf Shenanigans! 🎅 Santa replaced his trusty conveyor belts with a new shelf system—but something’s not quite right. Can you uncover the edge cases in how toys are placed and retrieved? Christmas depends on your testing skills! 🛠️✨ 👉 fast-check.dev/blog/2024/12...

🎄 Day 14: Compression Chaos! 🎅 Santa’s elves designed a compression algorithm to save space for the ever-growing pile of children’s letters. But Santa fears it might have bugs! Find a piece of text that breaks the system and proves there’s a flaw 🎁✨ 👉 fast-check.dev/blog/2024/12...

🚀 New patch release for fast-check! This update enhances stability, ensuring better reliability when working in environments with malformed or partially corrupted globals 💪