# John Wang

> Personal website of John Wang — co-founder / CTO of Assembled, previously an early engineer at Stripe. Writing about AI, engineering, and startups. Also co-created 143.dev, open-source coding-agent infrastructure.

John Wang is the co-founder and CTO of [Assembled](https://www.assembled.com), where he builds software that transforms customer support. He was an early engineer at Stripe (~employee 100), a co-founder and Chief Engineer at Zinc, and an active Ruby on Rails contributor (mostly ActiveRecord). He studied Computer Science at MIT. His writing focuses on AI systems, engineering craft and leadership, and practical lessons from scaling startups — aimed at engineers and technical executives.

## Blog

- [How Claude's watermarking (probably) works](https://johnjwang.com/post/2026/08/12/how-claude-watermarking-probably-works/): reverse-engineering Anthropic's Claude watermark from first principles — later confirmed correct by Anthropic's announcement that it uses SynthID-Text.
- [Cheap software won't make engineering cheap](https://johnjwang.com/post/2026/05/31/cheap-software-wont-make-engineering-cheap/): why engineers who know how to build quality systems become more valuable as AI writes more of the code.
- [Why we built 143](https://johnjwang.com/post/2026/06/30/why-we-built-143/): why Assembled built open-source coding-agent infrastructure so non-engineers can fix real product issues.
- [Number of tokens shouldn't be the only metric](https://johnjwang.com/post/2026/05/06/tokens-shouldnt-be-the-only-metric/): rethinking how we measure LLM output beyond token counts.
- [Why are executives enamored with AI but ICs aren't?](https://johnjwang.com/post/2026/03/27/why-are-executives-enabled-with-ai-but-ics-arent/): on the incentive and visibility gap between executives and ICs around AI adoption.
- [Time](https://johnjwang.com/post/2026/05/29/time/): reflections on time, compounding, and long-term building.
- [Mamba-3](https://johnjwang.com/post/2026/03/21/mamba-3/): an engineer's walkthrough of the Mamba-3 architecture.
- [Five opinions on building things well](https://johnjwang.com/post/2023/10/23/five-opinions-on-building-things-well/): what mortise-and-tenon joinery taught the author about building lasting software.

## Pages

- [Home](https://johnjwang.com/): bio, current work, and selected writing.
- [Blog archive](https://johnjwang.com/blog/): all posts, including external writing.
- [Work](https://johnjwang.com/work/): open source projects (143.dev, quickselect, Wallace), economics research, and Rails contributions.

## For machines

- Full-text RSS: [https://johnjwang.com/index.xml](https://johnjwang.com/index.xml)
- Every page is also available as markdown by appending `index.md` to its URL (e.g. [https://johnjwang.com/index.md](https://johnjwang.com/index.md)).