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Show HN: Get your coding agent off ~2019 JavaScript, onto modern web primitives

75 points paulirish 1 hour ago 28 comments

Browsers natively handle a lot of what used to take 50 lines of JS (or a dependency): `CSS.highlights` for text range highlighting without <span>s everywhere, `<dialog>` and showModal() give you backdrops and ideal focus management, `field-sizing` to auto-grow textareas as the user types.. (Something yesterday's ftrain post touched on [0])

Models know about some of these by name, but consistently won't default to using the platform-native solution and instead prefer the incumbent <div>+JS based pattern. We started an effort in Chrome to supplement coding agents with this key domain knowledge and we're shipping our 1.0 today, in collaboration with Firefox, MDN, and Edge.

200+ guides (~1.7MB) of curated, hand-crafted implementation best-practices from web experts, updated as the web evolves. (Open source, obv, so.. we'll welcome your bikeshedding ;) Readable versions here: [1]

I've spent the last 9 months obsessing over how to ship this as an agent skill + (Agentic RAG) CLI without blowing up your context window. (Or cedeing activation mechanics to MCP dynamic tool search). The skill description is minmaxed for activating on relevant frontend tasks. The RAG work I'm pretty proud of… originally a 500mb native stack down to a ~7MB pure-JS package, ~10ms search on your CPU.

We just introduced a deterministic 'legacy-scan' (trained on 30k github repos) to identify old 'n dusted patterns that your agent can modernize. (92% avg precision on held-out repos.)

People make a lot of claims about what coding agents are good/bad at. We wanted receipts, so we invested heavily in eval infra [2] to help us hill-climb, but also to identify when knowledge is common enough we can prune our guides. (Ofc, some of the things we thought AI didn't know turned out to be wrong :) We run codex/claude/agy against 200 tasks without the skill and then with.. In total ~1,700 playwright/AST-based assertions. Agents go from 55% pass unguided to 92% guided.

Try it out:

    DISABLE_TELEMETRY=1 npx modern-web-guidance@latest install
    DISABLE_TELEMETRY=1 npx modern-web-guidance@latest search "animate dialog modal"
    DISABLE_TELEMETRY=1 npx modern-web-guidance@latest legacy-scan ./src
If you spot something wrong or weird, give us a holler!

Longer write-up on the 1.0: https://developer.chrome.com/blog/modern-web-guidance-v1

---

0: https://news.ycombinator.com/item?id=50416456

1: https://developer.chrome.com/docs/modern-web-guidance/guides

2: https://googlechrome.github.io/modern-web-guidance-src/

phyzix5761 1 hour ago | parent

"Best Practices" are pretty much dead in the AI era. Pretty soon no one is going to read any of the code AI produces and that's a scary thought.

natorion 1 hour ago | parent

Best practices are not dead if they result in better user experience. The focus is less on developer ergonomics though - true that.

paulirish 1 hour ago | parent

IMO maintainability is the next frontier. If we just allow coding agents to accrete 1k-LOC solutions to problems, the codebases run quick away from our ability to maintain _some_ level of understanding.

So I'll take a 1-line CSS solution over 60 lines of ResizeObserver/setTimeout business. But.. best practices for frontend isn't just the code.. it's ensuring quality UX, that keyboard navigability works, that layout doesn't shift on users.

brlewis 57 minutes ago | parent

>Pretty soon no one is going to read any of the code AI produces and that's a scary thought.

This is a misconception. Have your favorite agent summarize this video for you: https://www.youtube.com/live/zcLPGC-tvgk?si=YR68aHlFESD053bh

ozim 41 minutes ago | parent

Ugh it is Uncle Bob, not going to torture AI with this guy.

But the fun part is that all of the proper software engineering practices are aimed at lowering amount of context a developer has to keep in his mind. So it directly applies to agent context. Less verbose code, less tokens to burn, separation of concerns, lower chance agent breaks something unrelated etc.

vik0 40 minutes ago | parent

>>Pretty soon no one is going to read any of the code AI produces and that's a scary thought.

>This is a misconception. Have your favorite agent *summarize this video for you*: https://www.youtube.com/live/zcLPGC-tvgk?si=YR68aHlFESD053bh

I can't tell if you're joking here

brlewis 23 minutes ago | parent

I am not generally against using AI to reduce the amount of information you need to pay attention to, and I was not joking. There are multiple places in that interview with good articulation of the reasons why software fundamentals still matter, and what happens when you don't look at at least some of the AI-generated code.

sublinear 44 minutes ago | parent

The "modern web primitives" are also not even necessarily the "best practice".

Browser-specific implementation gotchas tend to take about a decade to iron out for reasons that never have anything to do with code quality. Users are fickle and so are browser vendors, but that's a different topic.

At the end of the day, there's just no escaping lots of manual testing across device and browser combinations if your goal is a polished result and not just something that "works".

AI has done nothing to make this problem go away. If anything, it's made it worse because people don't even want to look at the code now!

halflife 1 hour ago | parent

Finally.

This is exactly what I need when I need it. The amount of pull requests I reviewed with a mess of codes that can be switched to 2 lines of modern features made me write such tools myself, only half assed since I have other things to do.

cyanydeez 57 minutes ago | parent

I treat all my code as some kind of stochastic machinery. So atleast one stage, I'd just tell an agent to go through and follow the guide.

But I'd not inject all this fluff into the wheels of the machine because it'd just take the "average" of these practices which would be just as useless.

simonw 53 minutes ago | parent

Distribution suggestion: in addition to the npm packages you have right now, set up GitHub Pages to publish a markdown index document of the skills at https://googlechrome.github.io/modern-web-guidance-src/skill... (currently a 404)

That index page should link to plain markdown versions of all of the documents, and should be designed for search with grep to find the right answers.

That way I don't have to install anything at all - provided my agent has the ability to make HTTP requests I can tell it "Look for tips on https://googlechrome.github.io/modern-web-guidance-src/skill..." and it will fetch the index, then navigate to the most relevant documents - no MCP or npm or installation required at all.

trvz 34 minutes ago | parent

What’s the point of modern Javascript without over complicating things?

kinlan 32 minutes ago | parent

https://developer.chrome.com/docs/modern-web-guidance/guides...

(we could make this clearer though)

paulirish 21 minutes ago | parent

Aye. I like the idea, Simon. The token cost of the index is high enough I wouldn't suggest the technique for regular use but.. agree that for occasional users it should suffice.

We'll make this happen. :)

nico 31 minutes ago | parent

> That way I don't have to install anything at all

It feels that something like this would be the holy grail of agents. A small agent that has only the minimum necessary built in knowledge. The rest, it just retrieves on the fly when it needs (+ caching)

It’s like storing pointers/links instead of the contents

paulirish 8 minutes ago | parent

In reality that's pretty much what we got here. Very progressive disclosure centric. There's a 'install' command exists because the ecosystem doesn't have good cross-agent ergonomics for installing skills. (Which bums me out).

But yeah.. big corpus of valuable context × minimal agent footprint = happy place.

advisedwang 42 minutes ago | parent

Chrome already has too much power in the browser standards world. The last thing we need is everyone's LLMs to follow Chrome team's guidance on how to do web development. This road leads back to "To view this site, please view in [DOMINANT BROWSER]"

philipwalton 35 minutes ago | parent

Mozilla Firefox and Microsoft Edge are also contributors to this project, so this is a cross-browser initiative to help improve how agents build for the web.

super256 32 minutes ago | parent

Calm your pitchfork, Mozilla and Edge are both part of Modern Web Guidance.

https://github.com/GoogleChrome/modern-web-guidance-src/blob...

0o777 28 minutes ago | parent

Both Mozilla and the Google Chrome team are part of the Web Baseline project and this project. They only recommend best practices supported by Chrome, Firefox, Edge, and Safari.

https://web-platform-dx.github.io/baseline/

zeroq 34 minutes ago | parent

What's the best way to introduce this to a Gemini chat?

fumar 24 minutes ago | parent

I added this a few months ago and Claude Doctor has not removed it. It must be working and getting use.

reedlaw 23 minutes ago | parent

These skills look better than most, but running my code through the legacy scan only found two issues. So while I still think training beats skills, I'm sure this has its place, especially with weaker models.

paulirish 13 minutes ago | parent

Yeah. The legacy scan is tuned to 1) focus on cases where there's a clearly detectable legacy pattern and 2) avoid false-positives. This means it only overlaps with 20% of all the skill's docs. (We'll probably get it to ~50% in another month).

In short: I 100% understand your disappointment. :) More coming soon like finding cases to update with Promise.withResolvers, the Array iterators, Object.groupBy, URLSearchParams, etc..

j45 17 minutes ago | parent

This is a great idea. I think while so much was being built out in the JavaScript ecosystem, awareness about the equivalent feature releases that were done to HTML, CSS, web components, and other technologies didn't keep pace.

Of course, it's not perfectly implemented the same in every browser, but that's nothing new.

cadamsdotcom 16 minutes ago | parent

Planning to give this one a wide berth.

The more "legacy code" is getting written everyday the more the web will be forced to remain backwards compatible...

PenguinRevolver 9 minutes ago | parent

I use Firefox after Chrome decided to become a bit of a pain to use on my powerful computers. I was unsure how bias the skills were for Chrome exclusive features, so I decided to ask ChatGPT to analyse the repo. I liked the answer it gave, so here it is: https://chatgpt.com/share/6af3712a-03cc-83eb-ad1f-66dd11c886...

gabrieledarrigo 3 minutes ago | parent

That's pretty cool!

On the other hand, a bit sad: programming nowadays is just arranging a bunch of Markdown files, possibly generated by another bunch of models.

Not so exciting, in the end.