“Loop engineering” is a hot buzzphrase after mentions of it by Boris Cherny (Claude Code’s creator) and Peter Steinberger (OpenClaw's creator) went viral on social media. Loops are now a key part of how we get AI agents to iterate at length to build software. In this letter, I’d like to share my 3 key loops, shown in the image below, for building 0-to-1 products. These loops guide not just how I build software, but also how I decide what software to build.
Agentic coding loop: Given a product specification and optionally a set of evals (that is, a dataset against which to measure performance), we can have an AI agent write code, test its work, and keep iterating until the code is bug-free and meets its specification. This idea of closing the loop took off around the end of last year, and it has been a game changer in enabling coding agents to work longer productively without human intervention. For example, over the weekend, I was building an app for my daughter to practice typing, and my coding agent could easily work for around an hour, using a web browser to check what it had built multiple times before getting back to me, without needing my intervention.
The engineering loop executes quickly. Every few minutes, the coding agent might build and test a new version of the software. I hear frequently from developers who are finding new ways to engineer more effective engineering loops. This is an active area of invention!
Developer feedback loop: In this loop, a developer examines the current product and steers the coding agent to improve it. Last year, a lot of developers (including me) were acting as the QA (quality assurance) function for our coding agents, manually finding bugs and then asking the agent to fix them. But with coding agents much more able to test their own code, the amount of time we need to spend on this function has decreased significantly. This allows us to make higher-level product decisions, such as what key features to offer, where the UI needs improvement, and so on.
The developer-feedback loop operates over time intervals between tens of minutes and hours — that's how frequently a developer might review a product and give feedback. In the case of the typing app, I changed my mind a few times about the visual design, what cat costumes she can unlock as she learns (she loves cats), and the user flow for a grown-up to log in and steer the child's learning experience.
When a developer has a clear vision for what to build, it is still a lot of work to translate that vision into a specification for a coding agent to implement. Further, after the developer has seen an implementation, they might update (or perhaps clarify) the spec to steer it toward what they want. If you find that the system repeatedly runs into certain problems, building a set of evals for the agent becomes useful.
AI-native teams are increasingly using AI to help shape product direction, for example, automating the gathering and analysis of usage data, summarizing written and verbal customer feedback, or carrying out competitive analysis. However, for pretty much all the products I’m involved in, I see humans as having a significant context advantage over current AI systems — we know a lot more than the AI system about the users and the context the product has to operate in — and thus humans play a critical role. Many people describe this human contribution as “taste,” but I prefer to think of it as humans having a context advantage, since that gives us a clearer path to helping AI systems get better. This also speaks to why this step can’t be automated: So long as the human knows something the AI does not, human-in-the-loop is needed to to inject that knowledge into the system.
External feedback loop: This includes a wide range of tactics like asking a few friends for feedback, launching to alpha testers, or putting the code into production with A/B testing. These tactics are usually slow, rarely taking less than hours and sometimes taking days or even weeks. This data informs the developer vision, which in turn continues to drive the detailed product spec, which in turn drives the coding agent.
With coding agents speeding up software development, more engineers are starting to play a partial product management role. For many engineers who are growing into this role, the hardest part is shaping the product vision and striking a balance between building (bridging the gap between vision and spec) and getting user feedback to evolve the vision. It is important to do both!
I will write more about how to do this in future posts, but for now, I find it encouraging that engineers are playing an expanded role (just as product managers and designers now do more engineering).
[Original text: The Batch]
React Doctor 这个代码检测工具和 Codex 的 Goal 简直是绝配!
今天用一条命令跑了 2 小时,直接干掉了 300 个代码质量与性能隐患,最后拿到了 100 分满分的健康分数,成就感满满。
顺便安利一下天才少年 Aiden Bai 和他打造的三个 React 质量与性能神器。他 16 岁独立开发 Million.js;18 岁带队入选 Y Combinator,为公司融资 1410 万美元。如今他做的这三款工具,刚好串联起了 AI 时代人机协同的完美闭环:
1. React Scan:浏览器里直接跑,哪个组件在重复渲染就用彩色边框高亮+闪烁,一眼就能看到性能浪费在哪。。
2. React Grab:网页上按 Cmd/Ctrl+C 点元素,直接复制出对应代码的文件路径、行号和组件栈,扔给 AI 让它精准修改。
3. React Doctor:专门扫描 AI 写出来的 React 代码问题(state、effect、性能、架构等),然后给项目打一个 0-100 的健康分数。能直接集成到 Codex、Cursor、Claude Code 里,或接入 CI 里自动运行。
现在最好的用法是直接在 Codex 里输入这条 Goal 指令:
/goal run "npx react-doctor@latest" and fix issues until you get a score of 100. do it properly without taking any shortcuts.
让它自己跑、自己修、自己验证,直到 100 分。
The “problem” with CS336 is not the ~22 hours of videos but the larger number of hours it takes to do the assignments.
But that is where most of the real learning occurs.
We’re reminded of @karpathy’s seminal tweet:
https://t.co/fvSeE2bDkE
2026 site: https://t.co/E1pzUSC6Tr
Ex-Google engineer explained AI agent loops, harness, evals in 20 minutes - better than 500$ courses.
trace every run → judge it with an LLM → diagnose → fix → ship.
That loop is how agents self-improve over time.
Agent loops + memory + harness + evals - thats the stack.
Watch it, then save the framework below.
Anime.js 4.5 is out and it's a fun one:
Introducing the @threejs adapter 🎉
- Up to 50% less code for 3D animations
- CSS transform-like API for 3D objects (rotate, skew…)
- Simpler material color animations
- Easy instanced mesh animations
- Stagger 3D
And so much more! ⬇︎
Announcing mattpocock/skills v1
- Achieved a 63% reduction in token cost for skill descriptions
- Split skills into model-invocable and user-invocable skills, adding /codebase-design, /domain-modeling, and /grilling
- (UPDATED) /writing-great-skills - rewritten from the ground up, encoding my skill-writing best practices
- (UPDATED) /diagnose -> /diagnosing-bugs - now model-invocable, awesome for fixing hard bugs
- (NEW) /ask-matt: a router skill that teaches you how all the engineering skills work together