vkuprin - 1d
I built Site Spy after missing a visa appointment slot because a government page changed and I didn’t notice for two weeks.
It watches webpages for changes and shows the result like a diff. The part I think HN might find interesting is that it can monitor a specific element on a page, not just the whole page, and it can expose changes as RSS feeds.
So instead of tracking an entire noisy page, you can watch just a price, a stock status, a headline, or a specific content block. When it changes, you can inspect the diff, browse the snapshot history, or follow the updates in an RSS reader.
It’s a Chrome/Firefox extension plus a web dashboard.
Main features:
- Element picker for tracking a specific part of a page
- Diff view plus full snapshot timeline
- RSS feeds per watch, per tag, or across all watches
- MCP server for Claude, Cursor, and other AI agents
- Browser push, Email, and Telegram notifications
Chrome: https://chromewebstore.google.com/detail/site-spy/jeapcpanag...
Firefox: https://addons.mozilla.org/en-GB/firefox/addon/site-spy/
Docs: https://docs.sitespy.app
I’d especially love feedback on two things:
- Is RSS actually a useful interface for this, or do most people just want direct alerts?
- Does element-level tracking feel meaningfully better than full-page monitoring?
As a (former) reporter, site monitoring is a big part of what I do on a daily basis and I used many, many such services.
I can attest that, at least from the landing page, this seems to be a very good execution of the concept, especially the text-based diffing to easily spot what changed and, most importantly, how.
The biggest hurdle for such apps however are 'js-based browser-rendered sites' or whatever they're called nowadays. How does Site Spy handle such abominations?
JS-rendered websites are sometimes even better, they usually have some sort of internal API that you can access directly instead of relying on the website styling which may change at any moment.
I'm a fellow reporter who needs to keep tabs on some websites. I used various tools, including running my own Klaxon[1] instance, but these days I find it easier to just quickly vibe-code a crawler and use GitHub Actions to run it periodically. You can make it output an RSS feed, email you, archive it with archive.today, take a screenshot, or trigger whatever action you want.
Thanks, that’s a really good question. Site Spy uses a real browser flow, so it generally handles JS-rendered pages much better than simple HTML-only polling tools. In practice, the trickier cases tend to be sites with aggressive anti-bot protection or messy login/session flows rather than JS itself. I’m trying to make those limitations clearer so people don’t just hit a vague failure and feel let down
Curious how you're thinking about getting around anti-bot protection. I scrape a lot and I've noticed many highly trafficked sites investing in anti-bot measures recently, with the rise of AI browsers and such. Still, cool idea, congrats on the launch.
I'm planning to add proxy rotation across different regions to help with geo-restricted content and rate limiting. Anti-bot is an arms race though — some sites just can't be monitored without solving a captcha, which isn't something I'm trying to do. Focused on making the common cases work well rather than promising to bypass everything.
What do you do now if you don’t mind sharing?
I like https://github.com/dgtlmoon/changedetection.io for this. Open source and free to run locally or use their Saas service.
There's also https://github.com/thp/urlwatch/ - (not aware of any SaaS offer - self-hosted it is).
Yep, urlwatch is a good one too. This category clearly has a strong self-hosted tradition. With Site Spy, what I’m trying to make much easier is the browser-first flow: pick the exact part of a page visually, then follow changes through diffs, history, RSS, and alerts with very little setup
Yep, changedetection.io is a good project. With Site Spy, I wanted to make the browser-first workflow much easier: install the extension, connect it to the dashboard, click the exact part of the page you care about, and then follow changes as diffs, history, or RSS with very little setup. I can definitely see why the open-source / self-hosted route is appealing too.
Does your project use changedetection.io behind the scenes? When I look at the _All Watches Feed_ the contents of the rss file include;
<?xml version='1.0' encoding='UTF-8'?>
<rss xmlns:atom="http://www.w3.org/2005/Atom" xmlns:content="http://purl.org/rss/1.0/modules/content/" version="2.0"><channel><title></title><link>https://changedetection.io</link><description>Feed description</description><docs>http://www.rssboard.org/rss-specification</docs><generator>python-feedgen</generator><lastBuildDate>Thu, 12 Mar 2026 10:10:10 +0000</lastBuildDate></channel></rss>Yes — it's a fork of changedetection.io. I went into more detail here: https://news.ycombinator.com/item?id=47349141. The RSS link you spotted was a leftover, already fixed
Changedetection has an extension too: https://chromewebstore.google.com/detail/changedetectionio-w...
Sure but this one has a MCP server, costs money, and was presumably made last night!
It's been around for a while and recommended by many. I tried it myself and it's okay.
Are you referring to OP's site? The domain was registered 2026-01-16 so it certainly hasn't been around for a while.
Looks cool and this can be self hosted and it is for free.
Nice will try this out!
I got claude to reverse engineer the extension and compare to changedetection and here's what it came up with. Apologies for clanker slop but I think its in poor taste to not attribute the opensource tool that the service is built on (one that's also funded by their SaaS plan)
---
Summary: What Is Objectively Provable
- The extension stores its config under the key changedetection_config
- 16 API endpoints in the extension are 1:1 matches with changedetection.io's documented API
- 16 data model field names are exact matches with changedetection.io's Watch model (including obscure ones like time_between_check_use_default, history_n, notification_muted, fetch_backend)
- The authentication mechanism (x-api-key header) is identical
- The default port (5000) matches changedetection.io's default
- Custom endpoints (/auth/, /feature-flags, /email/, /generate_key, /pregate) do NOT exist in changedetection.io — these are proprietary additions
- The watch limit error format is completely different from changedetection.io's, adding billing-specific fields (current_plan, upgrade_required)
- The extension ships with error tracking that sends telemetry (including user emails on login) to the developer's GlitchTip server at 100% sample rate
The extension is provably a client for a modified/extended changedetection.io backend. The open question is only the degree of modification - whether it's a fork, a proxy wrapper, or a plugin system. But the underlying engine is unambiguously changedetection.io.
Fair point, and I should have been upfront about this earlier. The backend is a fork of changedetection.io. I've built on top of it — added the browser extension workflow, element picker, billing, auth, notifications, and other things — but the core detection engine comes from their project. That should have been clearly attributed from the start, and I'll add it to the docs and about page.
changedetection.io is a genuinely great project. What I'm trying to build on top of it is the browser-first UX layer and hosted product that makes it easier for non-technical users to get value from it without self-hosting and AI focus approach
P.S -> I've also added an acknowledgements page to the docs: https://docs.sitespy.app/docs/acknowledgements
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I use RSS to get updates from a ll the stuff I read online at once, and thought this would be nice for those websites that don't already have an RSS feed, but... Perhaps I'm stupid, but I can't actually find the RSS output? And searching for RSS on https://docs.sitespy.app/docs returns no hits.
Not stupid at all — the docs were missing an RSS page, which is on me. I've just added one: https://docs.sitespy.app/docs/dashboard/rss. RSS feeds are available per watch, per tag, or across all watches from the dashboard. Thanks for flagging it, this is exactly the kind of feedback that helps
Calls to mind a long forgotten, and perhaps one of the most useful bash scripts I've written which addressed this issue in a very rudimentary way; Curl a url, hash the result to file, compare the current hash to the saved hash from the previous run and generate an email on diff.
My goal was to monitor the online release of tickets for the 2009 Scion Rock fest (luckily no js, or even Adobe Flash[!] in use), and it worked brilliantly to that end.
[grammar]
This is directly useful for financial data monitoring. I've been thinking about watching specific elements on energy report pages (EIA weekly inventory releases, OPEC statements) rather than scraping the full page. The element picker + RSS output is exactly the right interface for that — pipe the change event straight into an NLP pipeline without the noise of a full page diff.
The RSS question: yes, RSS is useful precisely because it's composable. It works with anything. Direct alerts are convenient but RSS is infrastructure.
RSS is a useful interface, but: "Do most people just want direct alerts?" Yes, of course. RSS is beloved but niche. Depends who your target audience is. I personally would want an email, because that's how I get alerts about other things. RSS to me is for long form reading, not notifications I must notice. The answer to any product question like this totally depends on your audience and their normal routines.
It's niche because some companies decided so.
you used to have native RSS support in browsers, and latest articles automatically in your bookmarks bar.
That's good reasoning, but the parent's point still stands?
If you design for email alerts you invite reply loops, permanent delivery failures, and all the headaches of scaling SMTP. RSS, while nerdy, offloads almost every operational hassle to the client and works fine for polling when instant delivery isn't mandatory.
Some users want to pipe these updates into scriptable things like Slack, bots, or custom dashboards, where RSS is much easier to handle than email. If you offer both, people will use whichever fits their workflow, and that isn't always predictable.
I added my employer's website RSS feed to the all-staff Slack channel. I find it useful, I don't know about others but no one has grumbled.
https://slack.com/intl/en-gb/help/articles/218688467-Add-RSS...
Nobody has mentioned, that FreshRSS [0] has built-in web scraper too. It is also easier to use (little bit, imho), than changedetection.io. Works like a charm for me - mostly window shoping thrift shops.
Kudos for the launch. Super useful for people tracking granular updates!
I've built something similar for the startup I'm working at, but across the web with a Natural Language Interface: https://parallel.ai/products/monitor. It can find diffs in previous content or find new pages pertaining to the query depending on the semantics. Hope people on this thread are able to derive value from it.
Does anyone here remember WinerWatch? The tool Mark Pilgrim wrote, that monitored changes to blog posts by (the notoriously trollish) Dave Winer? It caused a big stir in the blogosphere in 2003, and Mark took it down very quickly after public blowback. I always thought it was pretty cool and he should have left it up.
One of the very few surviving posts on the matter: https://burningbird.net/forget-the-law-forget-the-technology...
What an interesting glimpse into the blogosphere. That post in particular is interesting, given the much larger discussions that followed it on essentially the same topic: how to decide what people can and can not say when there are those who ruin the commons. I'm thinking of Twitter/X's Community Notes feature and the many reputation mechanisms people put in place, and the subsequent griping of community politics that arise from those mechanisms...
i've actually been looking for something like this. full-page change monitors get noisy really fast, especially on sites with lots of small UI changes.
being able to watch a specific element sounds way more useful in practice (price blocks, availability text, etc).
curious how fragile the element tracking is though. if the site slightly changes the DOM structure or class names, does the watcher usually survive or do you end up reselecting the element pretty often?
The selector is stored as a CSS path and matched against the fetched HTML on each check — so as long as the element's structure and nesting stay roughly the same, minor layout changes don't usually break it.
The fragile cases are sites that generate class names on every build (React/webpack/vite apps often do this) — those selectors will just stop working.
For semantic elements like price tags, availability text, or content blocks, they tend to be stable enough that it's not a real problem day-to-day. And if a filter stops matching entirely, the watch flags with error message it rather than silently giving you empty diffs.
that makes sense. the error flagging is a nice touch — silent failures are usually the worst part of these tools. i've also run into the “random class name” problem on a lot of modern frontends. have you experimented with more semantic selectors (text anchors, attributes, etc) as a fallback, or do you try to keep it simple on purpose?
Yeah, semantic anchors are definitely the right direction — [data-testid], aria-label, or text proximity tend to survive rebuilds much better than class paths. The picker leans towards CSS right now but that's something I want to improve.
The harder problem is auth-gated content — Instagram feeds, dashboards, paywalled pages. Browser Steps handles it today (you can script login flows), but honestly I think the real fix is AI-assisted interaction. A small cheap model that can find what you care about without needing a brittle selector at all. That's where I want to take this — less "maintain a CSS path", more "here's what I'm interested in, figure it out...
that direction makes a lot of sense. selectors always end up turning into maintenance work sooner or later.
the idea of a small model just identifying “the thing that looks like a price / status / headline” feels much closer to semantic detection than DOM-path tracking
curious though — would you run that model on every check, or only when the selector fails? seems like a nice hybrid approach to keep things cheap.
Yes! Exactly this direction — the hybrid fetch is already live: plain HTTP first, Chromium if the content looks off. LLM semantic targeting is the next step, but only triggered when a selector breaks, not on every check — too expensive otherwise.
Quick feedback:
1. RSS is just fine for updates. Given the importance of your visa use-case, were you thinking of push notifications?
2. Your competition does element-level tracking. Maybe they choose XPath?
Yep, Site Spy already has push notifications, plus email and Telegram alerts. I see RSS as the open interface for people who want to plug updates into their own reader or workflow. For urgent things like visa slots or stock availability, direct alerts are definitely the main path.
And yeah, element-level tracking isn't a brand new idea by itself. The thing I wanted to improve was making it easy to pick the exact part of a page you care about and then inspect the change via diffs, history, or RSS instead of just getting a generic "page changed" notification
I think it's very useful cause i also had these types of miss fortunes in the past and i don't want to experiance these again at all
I have my own hobby RSS server built around the Google Reader API. Two of my plugins are pretty similar to what you described: one checks a page’s current state against the last saved version and publishes an entry if anything changed, the other is basically a CSS selector-based feed builder. Always good to see RSS content here, thanks for posting!
On your questions: some people prefer RSS, others email, and services exist to convert between the two in both directions. My own rule of thumb is email for things that need actual attention and RSS for everything that can wait. If you’re thinking about turning this into a service, supporting both would make sense since people are pretty split on this.
Looks good! RSS is underrated for this honestly. I'd rather check a feed when I want than get pinged at 2am because a sidebar changed.
Something I was planning on building but never got round - if anyone wants to do it then feel free to use this idea.
Lots of companies really have no idea what javascript is being inserted into their websites - marketing teams add all sorts of crazy scripts that don't get vetted by anyone and are often loaded dynamically and can be changed without anyone knowing.
A service that monitors a site and flags up when the code changes - even better if it actually scans and flags up malicious code.
This is a very common use case, I myself hand-coded something similar 13 years ago [1]. Kudos for the choice of RSS!
Will this work on websites that may have Cloudflare captchas popping from time to time?
This is cool. I'd use it to track when state wildlife agencies update their regulation pages — those change once a year with no announcement and I always miss it. Element-level tracking would be perfect for that vs watching the whole page. To answer your question: I'd want both RSS and direct alerts (email/push) depending on urgency.
That looks nice, I use the free plan of https://visualping.io for some software changelogs, RSS feeds are a paid feature. Will check this out.
Yeah, RSS is free on all plans — it felt like a core feature, not an upsell