Build a read-only browser extension that adds a missing filter to a website

Siyabulela Nato, a data engineer in Johannesburg, had a weekly question at work that took many clicks on a private site: pick report types, a date range and a state, then scan the list. He gave Claude Code the Chrome DevTools MCP server so it could open the page, do the task once by hand and list the network requests behind the list and filters. Claude then wrote a Manifest V3 extension for Edge and Chrome with one content script, no permissions and GET requests only to the same site, adding a filter panel with a count, linked results, copy as table and a shareable link. He repeated the build on the public SeeClickFix 311 site to show the method, asking it to respect the documented 20 requests a minute and back off on 429 replies.

He says the work version answers the weekly question in one panel and that he checked its count against the site's own numbers. On SeeClickFix, a 30-day search of New Haven's map area fetched 322 requests across four pages in 13 seconds, and a graffiti and dead animal filter showed 8 in the panel and 8 from a direct API call. The build took an afternoon and the public version is on GitHub.

The extension only sees data the page can already see, and it works best when the page loads its list from an API; scraping the page itself breaks when it changes. Company browsers often block unpacked extensions, so a team rollout usually goes through IT. Check the site's terms and rate limits first.