How to Learn Fuzzing for Smart Contract Security | From Recon
I'm Alex from Recon. Three years ago, we built Chimera, a Solidity Framework that lets you write your tests once and run them across multiple tools such as Foundry, Echidna, Medusa, and Halmos. More recently, we built the Recon Fuzzer.
Over these three years, we've taught these techniques to students and to members of our team for invariant testing engagements. Our company has protected roughly $30 billion of TVL for our customers, and last year we prevented a critical mainnet exploit that would have stolen about $20 million.
Below are the best videos to watch to learn fuzzing. They'll take you from zero to actually fuzzing and securing — or breaking — the protocols you're building.
From idea to Fuzzing
https://www.youtube.com/watch?v=3A7aa5B8aak
This 30-minute video condenses three years of work. It shows you the entire workflow of identifying what to test, then fuzzing it in a progressively more thorough manner.
You’ll start with something really basic — just a function for price — then write a test, deploy the contracts, and run a basic test. From there, you expand it into a fuzz test, then extend it further into a stateful test with Echidna so you can actually break it.
Finally, to gauge maximum impact, you convert that same test into an optimization test, still with Echidna.
What fuzzing for Security Research actually looks like
https://www.youtube.com/watch?v=F-tg2bEfjik
This is essentially the live-coding version of the talk above. With the first video, you'll understand the ideas but won't necessarily code them step by step, since only snippets are shown. In this video, you code the full exercise live, so you can see how long it takes and how much work it involves.
Using Optimization tests to constraint the impact of a bug
https://www.youtube.com/watch?v=E-1O0BGh8JY
This video is tied to the realization that some bugs shouldn't be expressed as assertions. They're better expressed as optimization properties. The video covers exactly that.
Once you've done the basics, set up fuzzing, and understood the workflow, watch this video for the additional insight: running optimization tests alongside assertion tests to protect a system even further.
Using Fuzzing and other techniques to Ship Protocols Safely
https://x.com/i/broadcasts/1BdxYqLoRgBxX
This is a holistic discussion on shipping Solidity systems safely, recorded with other leaders in the space. Customers who handle billions of dollars of TVL and who have built tens, if not hundreds, of smart contracts over their careers. The discussion uses fuzzing, AI, audits, and developers as tools, then goes deep into what it actually means to ship a protocol safely.
Once you understand fuzzing and testing, this video gives you the context for what you actually want to do with those skills.
Bonus Videos
These videos are more motivational and insightful, around the context of fuzzing for security rather than just about fuzzing.
34 tips to crush it in 2026: https://x.com/getreconxyz/status/1998648970013286852/video/1
This was very popular when I released it in December last year, with over 15k views.
The advice in this video is especially relevant if you're a security researcher, solopreneur, or small company — that's the experience this talk speaks to most directly. Hopefully you'll pick up a few gems.
Setting up governance in a safe way
https://x.com/getreconxyz/status/1885249716386226572
Nearly every protocol exploited in the past six months has been tied in some way to governance. There are so many governance and private-key-related exploits, and this two-hour video talks exclusively about that: mitigating these completely unnecessary types of exploits through a proper setup.
To make the video interesting, my friends and colleagues join the conversation. Everyone has the goal of securing governance setups, but each guest offers a different perspective, so you can pick and choose the combination that actually makes sense to you.
Reverse engineering bytecode for security
https://x.com/getreconxyz/status/1893707255977324960
This is a pretty deep talk about various tools that let you take some random bytecode and generate interfaces and function definitions — essentially reverse-engineering the source code of a smart contract. The overarching goal is security: you want to figure out what the contract does and how you can interact with it so you can, for example, fuzz it.
It's one of the more interesting talks. It showcases tools built by insanely smart engineers, completely for free and all open source. Not only is the talk cool, the speakers are cooler, and the tooling is amazing.
About Recon
Leaders in Stateful Fuzzing for Solidity Smart Contracts. Customers total over $30 BLN in TVL and $20 MLN of live exploits prevented. Authors of the Chimera framework, used in the majority of open source Solidity Stateful Fuzzing campaigns.
