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

250 points paulirish 6 hours ago 71 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 6 hours 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 6 hours 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 6 hours 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.

aidos 4 hours ago | parent

Once again, thank you for all the work you and the team have done to improve the web and the experience for developers working with it.

noosphr 3 hours ago | parent

You just regenerate the codebase, like how you do a recompile in C. Writing code is 2026 is worth as much as writing machine code was in 1996.

brlewis 5 hours 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 5 hours 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 5 hours 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 5 hours 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.

drawfloat 4 hours ago | parent

Why don't you just quote them then? Or quote whatever the LLM you used gave.

sublinear 5 hours 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!

zeroq 4 hours ago | parent

Exactly.

I've recently finished a browser game specifically targeting an old iPad Air 1 we had lying around the house.

I had a working version after a weekend, but it took me a month to make it run smoothly on an over 10 years old mobile device. And the most recent browser available is almost 10 years old.

Surprisingly I didn't missed too many "modern" JS features, as these were mostly functional programming oriented which doesn't play well with optimization anyways, and the ES6 was more than enough as a programming platform.

Anyway, what I'm trying to say is that "the best practice" should be making your apps fast and accessible - as much as you can without having to sacrifice something you value - instead of chasing the latest and shiniest.

Don't be a fashion driven developer. :)

halflife 6 hours 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 5 hours 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 5 hours 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 5 hours ago | parent

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

kinlan 5 hours ago | parent

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

(we could make this clearer though)

paulirish 5 hours 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. :)

jph00 5 hours ago | parent

If you rename that file to "llms.txt" it'll be a bit more discoverable.

kinlan 4 hours ago | parent

yeah that's fair. the infrastructure we are on isn't the most flexible (we will soon move to a newer more custom platform but that's a little way a way)

kohukohunui 4 hours ago | parent

It looks like the markdown has cross references that assume that the cli approach is used, it would be nice to separate the content from the tooling to access.

nico 5 hours 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 5 hours 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.

mtrovo 4 hours ago | parent

If created properly, skills are already something like that. You have a front matter summary always available to the agent. The agent can request the full skill content on demand, which might contain additional linked documents with details about APIs and schemas being used, deeper documents about niche subtopics, scripts to help with subtasks, etc.

advisedwang 5 hours 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 5 hours 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.

troupo 2 hours ago | parent

That's why it seems to skip the most egregious of Chrome-only APIs and focuses on areas where there's large cross-browser agreement.

philipwalton 55 minutes ago | parent

Cross-browser compatibility has been a guiding principle for this project from the start. See: https://youtu.be/bo3i0FzDUYo?si=EqIgY_Kh_r_hSgdE&t=686

Also Mozilla only joined in the last few weeks, so they haven't yet had a big influence on the project (though I expect they will going forward).

super256 5 hours 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 5 hours 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/

xnx 4 hours ago | parent

Not my opinion, but I do wonder if sharing from a different repo would feel more neutral.

tonymet 2 hours ago | parent

Let the best API win. why hold them back?

girvo 46 minutes ago | parent

Because Google/Chrome should’ve been split up under antitrust grounds, instead of the “too hard let’s not bother” judgment they ended up with.

tonymet 17 minutes ago | parent

because the $200m+ spent public & private on the Microsoft antitrust did a public service? talk about a farce and a waste of resources.

Google hardly has a monopoly. The app experience is very diverse. If anything, Apple is much more anticompetitive than Google.

Or is it that you resent any success?

Google gives away Chromium for free. Microsoft & Linux distros use it.

Thanks, this is one of the most laughable comments of the day.

zeroq 5 hours ago | parent

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

paulirish 4 hours ago | parent

Gemini web? Probably simonw's strat from the top comment.

There's a plugin for Antigravity that's listed on initial setup (yay bundleware! :) but... yeah if you're using consumer gemini, i'd switch to the Tasks mode because it's more agentic nature helps.

In fact I just did this and it works. :p It regular Gemini, it said it did but kinda liked :) So there it'd be

> Create a perfect HTML contact form with address fields. Check https://developer.chrome.com/docs/modern-web-guidance/guides... — read completely, don't stop at truncation.

yh11 3 hours ago | parent

why would you ever use gemini for coding at all

zeroq 3 hours ago | parent

Argon is not available in agy for Pro users.

fumar 5 hours ago | parent

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

reedlaw 5 hours 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 5 hours 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 5 hours 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 5 hours 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 5 hours 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 5 hours 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.

chalmovsky 4 hours ago | parent

Amazing! I'm just writing an article about how Alex Russell's quote about 'React being a legacy technology' got, unfortunately, totally ignored.

And now this just fell in my lap! Some of the arguments I wanted to make seem to be provide here. Didn't have a chance to take a proper look at it, but it looks very promising and nice!

Thank you!

surround 4 hours ago | parent

Here's a list of browser features the skills will tell your agent to use that are stable in Chrome but not supported by Firefox and Safari:

  CSS @function
  CSS calc-size()
  CSS interpolate-size
  CSS corner-shape
  CSS border-shape
  CSS flex-wrap: balance
  CSS text-fit
  CSS text-decoration-skip-spaces
  CSS scroll-axis-lock
  CSS scroll-target-group
  CSS :target-current
  CSS scroll-initial-target
  CSS container scroll-state queries
  scrollsnapchange event
  scrollsnapchanging event
  HTML focusgroup
  Element.startViewTransition()
  CSS view-transition-scope
  Interest Invokers (interestfor)
  LanguageModel (Prompt API)
  LanguageDetector
  Translator
  Summarizer API
  Window.fetchLater()
  Speculation Rules API
  Long Animation Frames API
  VisibilityStateEntry
  PerformanceSoftNavigation
  InteractionContentfulPaint
  Connection-Allowlist
  CSS url() integrity() modifier
  HTML meta name="text-scale"
  HTML template for
  HTML processing instructions
  PasswordCredential
  Promise-returning scroll methods
  Web App Origin Migration
  Local Network Access permissions
  Request.targetAddressSpace
  beforeinstallprompt event
To be fair, the skills also recommend ~11 features not supported by Chrome itself. And the project does seem concerned with compatibility: "Guiding models to use sensible, lightweight fallbacks."

philipwalton 3 hours ago | parent

> Here's a list of browser features the skills will tell your agent to use that are stable in Chrome but not supported by both Firefox and Safari:

To be clear, the skills document how to use these features to solve common use cases, and then they give your agent a full browser support table for any APIs mentioned that are not Baseline Widely available -- and then your agent can decide whether to use them or not, based on your site's browser support requirements.

In most of these cases a cross-browser fallback is also documented.

surround 3 hours ago | parent

The line between documenting and instructing is blurry in many cases. For example, these statements are meant to document best practices to the agent, but they sound like instructions:

"DO use fetchLater()..."

"Your own code MUST call fetchLater() directly..."

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

But yes, the skills do document compatibility and fallbacks well.

philipwalton 3 hours ago | parent

Agreed the line can be blurry, but I want to stress that the goal of this project is NOT to push Chrome-only APIs on users.

The mental model we've been using on the team is:

If you hired an expert web development consultant to build X, what would they recommend as a best practice? When does it make sense to use the new API (because it provides real benefits) vs. when does it make sense to wait until it's available everywhere?

To use your `fetchLater()` example, this is a case where the `fetchLater()` API legitimately solves a very real problem for people trying to build accurate analytics or telemetry features, see: https://nicj.net/beaconing-in-practice/

And lots of companies actually are already using `fetchLater()` in production now because of its increased reliability.

cma 2 hours ago | parent

I think I can guess from corporate incentives why Chrome supports fetchLater and some others don't.

philipwalton 1 hour ago | parent

It's currently being added to WebKit: https://github.com/WebKit/WebKit/pull/73271

Regarding corporate incentives: I was involved in the design of this API, so I know the history. It was proposed many years ago as a solution to make it easier for RUM analytics providers to measure Core Web Vitals metrics that needed to account for more than just page load (e.g. layout shifts and slow interactions can happen any time, not just during page load).

The RUM providers we worked with were reluctant to wait until page unload to send telemetry data because it resulted in too many lost beacons, so what they do instead is send beacons every few seconds with the most up-to-date payload.

The `fetchLater()` API enables them to send just one beacon, which is good for users and also reduces their server load.

hatthew 2 hours ago | parent

In my experience, it's difficult to suggest something to an LLM in a way that it doesn't interpret as a command, unless I explicitly list conditions (which it will take as law rather than guidance).

lelandfe 27 minutes ago | parent

The default behavior for this "web best practices" tool which steers people away from "legacy patterns" has agents using Limited Availability features with complex and nuanced[0] fallbacks?

This would be deeply surprising to me, and I am the target audience for this repo. I'd expect the default here to be Widely Available only with some opt-in for the courageous. I don't know that I'd even enable it.

[0] https://github.com/GoogleChrome/modern-web-guidance/blob/4dd...

hackingonempty 3 hours ago | parent

How about details/summary?

philipwalton 1 hour ago | parent

The details/summary features are covered in the accordion guide here: https://developer.chrome.com/docs/modern-web-guidance/guides...

If you scan to the bottom of the guide under the "Fallback strategies" section, you can see the recommendations for how to deal with the aspects of details/summary that aren't Baseline widely available (e.g. mutually exclusive details).

dallen33 3 hours ago | parent

Paul Irish?? There's a name I haven't though about in ages! I remember following you on Twitter and your website was full of amazing information. Hope you're doing well!

internet2000 3 hours ago | parent

NO THANK YOU. Do not want my agents to contribute to the Chrome monoculture. Chrome is the new IE6.

tonymet 2 hours ago | parent

no it's not. they publish the APIs. IE was bad because ActiveX was proprietary and private.

adzm 3 hours ago | parent

I find this very useful as a human as well

mococa 3 hours ago | parent

More Chromish on web? No thanks.

tonymet 3 hours ago | parent

I recommend saying "contemporary" or "suggested" for transient proposals like this. Having modern change every few years is ambiguous and cliche .

These concepts are new, so no one knows if they are any good. They're not modern -- who knows if they will even be put to use?

"contemporary", "proposed", "suggested", "compatible" are better fit. I wouldn't dare use "advanced" because many APIs and proposals actually regress earlier behavior.

pyrolistical 3 hours ago | parent

I asked my agent to look at that list and only apply things that work on chrome, Firefox, safari iOS and safari macos

Came up with a good list for my project

codepoet80 2 hours ago | parent

I want the opposite of this. I want compatible code -- which is really hard, when there are so many eras to target. So far AI has done a great job of finding that sweet spot -- why would I want a tool that encourages the agent to write less compatible code?

SoftTalker 1 hour ago | parent

Remeber, the features you don't use are the ones you don't have to support, or scramble to replace when they are deprecated.

Keep your effing websites simple.

SoftTalker 1 hour ago | parent

> We wanted receipts, so we invested heavily in eval infra to help us hill-climb, but also to identify when knowledge is common enough we can prune our guides.

Good god.

paulirish 1 hour ago | parent

what? oh. I mean.. I wrote it all with my lil fingies, but I did pack some jargon in there. :) More plainly...

We built rigorous tests to verify this actually works, and to know when models no longer need the advice.

rewgs 49 minutes ago | parent

"hill-climb" is the most aggressively LinkedIn speak I've ever encountered in the wild.

dazhbog 1 hour ago | parent

I ask my agent to write ES5 as I am more comfortable with it.. i need to read and maintain that slop somehow..

ggregoire 7 minutes ago | parent

Is there a similar project for React? There are so much bad React code and wrong/old design patterns on the internet that surely ended in the training datasets