The archive · Developer & Business Tools · Product decision · 2025-2026
JSX Tool's browser-IDE bet: 111-pt Launch HN, then YC F25 firm pivots to Coasts
YC F25 Chrome-extension IDE: click React elements and prompt LLMs with exact source context; 111-point Launch HN, later redirected to agent infra as Coasts.
JSX Tool
What the business is
JSX Tool is an in-browser React IDE, shipped as a Chrome extension, that maps any rendered element back to its exact line of JSX so developers can edit code or hand an LLM precise DOM, style and component context without leaving the browser.
How it started
New York childhood friends Jamie Sunderland and Dan had built projects together for nearly 20 years. Sunderland was a second-time YC founder - he had co-founded Cheqout (YC W21), a QR-ordering platform that grew to over 250 restaurants and $30M in GMV during the pandemic, then worked as a software engineer at Y Combinator itself. After years of React development, Sunderland concluded that AI could not do precise UI work because it never saw the real DOM-to-source relationship, so he hacked together an inspector connecting JSX and HTML in both directions and the pair entered YC's Fall 2025 batch with it.
What happened
JSX Tool publicly launched on Hacker News on 2025-11-12 and drew 111 points and 83 comments, with the founders explaining months of dogfooding, an open-sourced dev server, and free non-AI IDE features with rate-limited AI prompting. A July 2026 Launch YC post introduced the fuller AI-first story: click any element, prompt an LLM with the exact source component, styles and React hierarchy, tag other page elements or files into the prompt, and keep a full IDE in the browser with TypeScript, Tailwind, ESLint and Prettier language servers.
How it ended up
No shutdown or acquisition has been announced. By 2026-09-04 the company's YC directory record - same founders, Fall 2025 batch, two-person team, active - presents the startup under a new name and product, Coasts, described as localhost service isolation and orchestration for git worktrees so multiple AI coding agents can build in parallel without port, database or environment conflicts. The JSX Tool launch remains listed under the company's launches on the same page.
Background
JSX Tool was a YC Fall 2025 startup founded by New York childhood friends Jamie Sunderland and Dan, who had worked on projects together for nearly 20 years. Sunderland was a second-time YC founder - his first company, Cheqout (YC W21), was a QR-ordering platform that reached over 250 restaurants and $30M in GMV during the pandemic - and he later worked as a software engineer at Y Combinator itself.
The product was an in-browser React IDE shipped as a Chrome extension. Its core claim was that LLMs fail at precise UI work not because they lack visual skill but because they never get proper context, so JSX Tool built a custom AST parser mapping JSX to the DOM in both directions: click any rendered element and jump to the exact source line, or prompt a model with the precise component, styles and React hierarchy behind what you clicked. A dev server with language servers for TypeScript, Tailwind, ESLint and Prettier was open-sourced.
JSX Tool launched on Hacker News on 2025-11-12, drawing 111 points and 83 comments, and followed with a July 2026 Launch YC post on its AI-first workflow including @-tagging of page elements and files into prompts. The free IDE features were designed to work without AI, with rate limits on the prompting features.
As of September 2026 the company's YC directory record is active and presents the same two-person Fall 2025 team under a new name and product, Coasts: localhost service isolation and orchestration for git worktrees, aimed at teams running multiple AI coding agents in parallel. The JSX Tool launch remains archived under the same company page.
What has to be true
- The traction is dated and concrete: 111 points and 83 comments on the 2025-11-12 Launch HN, plus a second launch on YC's channel on 2026-07-27.
- It is a repeat-founder case: Jamie Sunderland had already taken Cheqout through YC W21 to 250+ restaurants and $30M GMV before working inside YC, then chose a devtools wedge.
- The technical wedge is original: bidirectional JSX-DOM mapping plus an open-sourced dev server, giving LLMs exact source context instead of screenshots or prose.
- The company's visible pivot - the same F25 record now sells Coasts, isolation tooling for parallel coding agents - shows how early bets get redirected as the agent market moves.
What can be applied
A YC slot is a licence to iterate, not a verdict on the first product: the same F25 record that launched JSX Tool now sells agent-infra tooling as Coasts.
Aftermath
As of 2026-09-04 the startup is live but transformed: the YC directory lists an active two-person company founded in 2025 in YC's Fall 2025 batch, now branded Coasts, with Jamie Sunderland as founder and CEO and Pete Koomen as YC partner. Coasts sells a localhost runtime that gives each git worktree its own isolated containerized environment so coding agents can work in parallel without clashing ports, databases or fragile per-branch setups. No funding round beyond YC or exit has been disclosed, and the JSX Tool extension's launch post remains visible under the same company record.
Sources
- Launch HN: JSX Tool (YC F25) - A Browser Dev-Panel IDE for React
- Launch YC: JSX Tool: In-Browser React IDE
- JSX Tool Launches: In-Browser React IDE
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