{"slug": "show-hn-building-ai-agents-client-side-javascript", "title": "Show HN: Building AI agents client-side JavaScript", "summary": "A developer has launched Buttercup, an open-source project demonstrating AI agents built entirely in client-side JavaScript that run in the browser, aiming to reduce infrastructure costs by eliminating server-side proxies and API calls. The project supports offline models via ollama/vLLM and embedded WebLLM, and will publish a weekly guide starting mid-September covering in-browser loops, multimodal vision, remote agent access, and multi-agent coordination.", "body_md": "Hey HN, most agent systems default to server-side Python inside containers and chain frameworks. I wanted to see how far we could push agent in the browser with vanilla JavaScript [https://buttercup.sh](https://buttercup.sh)\n\nThe reason this is interesting is because agent loops in the browser keeps infrastructure costs low. No need for proxy or API calls. And ollama/vLLM can be used for 100% offline. Also WebLLM for embedded. We need to consider CORS, API keys for remote models, access to visual state, and handling remote tool calls. I am working on a guide with references in vanilla JS. This is a short-lived guide starting mid-September with weekly topics.\n\nDraft topics starting mid-September:\n\nIn-Browser Loops: Function calling, and deterministic multi-turn loops running purely in the browser runtime. Vision (Multimodal): Capturing viewport screenshots using browser APIs. Remote Agent Access & Transports: Connecting the in-browser agent to remote agents. Multi-Agent Coordination: Lightweight client-side agent, specialist delegation, and running concurrent sub-agents without locking the browser UI thread.\n\nEverything is open source, zero-install, and runnable directly in the browser. Would love feedback from the HN community on agents running in browsers.\n\nComments URL: [https://news.ycombinator.com/item?id=49557409](https://news.ycombinator.com/item?id=49557409)\n\nPoints: 1\n\n# Comments: 0", "url": "https://wpnews.pro/news/show-hn-building-ai-agents-client-side-javascript", "canonical_source": "https://news.ycombinator.com/item?id=49557409", "published_at": "2026-09-03 21:34:31+00:00", "updated_at": "2026-09-03 21:53:08.302218+00:00", "lang": "en", "topics": ["ai-agents", "ai-tools", "ai-infrastructure", "developer-tools"], "entities": ["Buttercup", "ollama", "vLLM", "WebLLM", "Hacker News"], "alternates": {"html": "https://wpnews.pro/news/show-hn-building-ai-agents-client-side-javascript", "markdown": "https://wpnews.pro/news/show-hn-building-ai-agents-client-side-javascript.md", "text": "https://wpnews.pro/news/show-hn-building-ai-agents-client-side-javascript.txt", "jsonld": "https://wpnews.pro/news/show-hn-building-ai-agents-client-side-javascript.jsonld"}}