How I wrote JustHTML using coding agents
December 18, 2025
Writing a full HTML5 parser is not a short one-shot problem. I have been working on this project for a couple of months on off-hours.Tooling: I used plain VS Code with Github Copilot in Agent mode. I enabled automatic approval of all commands, and then added a blacklist of commands that I always wanted to approve manually. I wrote an agent instruction that told it to keep working, and don’t stop to ask questions. Worked well!Here is the 17-step process it took to get here:
Source: How I wrote JustHTML using coding agents – Friendly Bit
A few weeks back, Simon and Wilson coined the term “vibe engineering” trying to create a distinction between the use of large language models to generate code that we simply run as-is, against the use of large language models as part of the software engineering process. This example he links to is an excellent example of vibe engineering.
Emil Stenström he’s written an HTML parser, which, if you know anything about HTML, is much more complex than it might initially appear. Here, Emil details his approach to working with large language models to produce a very complex piece of software. Emil is a software engineer, but he observes that:
Yes. JustHTML is about 3,000 lines of Python with 8,500+ tests passing. I couldn’t have written it this quickly without the agent.
But “quickly” doesn’t mean “without thinking.” I spent a lot of time reviewing code, making design decisions, and steering the agent in the right direction. The agent did the typing; I did the thinking.
That’s probably the right division of labor.
