stagewise puts a coding agent inside the app you are already looking at
Most AI builders dazzle on a demo and stall on a real codebase. stagewise (YC S25) took the opposite route - it lives in your running app on localhost, where you click an element and it edits the actual source.
Every AI app builder has a great first date. You describe a landing page, and thirty seconds later something colorful appears on screen. The trouble starts on the second date, when the project stops being a demo and becomes a codebase - one with tests, an API, a deploy pipeline, and a thousand small decisions already baked in. The magic that felt effortless on a blank canvas turns brittle the moment there is something real to break.
stagewise, a company in Y Combinator's Summer 2025 batch, was built around that second date. Its pitch is narrow and specific: a frontend coding agent that runs inside your own web app while it is running on localhost. You click on a button that is the wrong size, type "make this shorter and move it left," and stagewise edits the actual source file. No copying screenshots into a chat window. No describing, in prose, a thing you are already staring at.
01 - THE BLIND SPOTWhy AI code editors keep fumbling the frontend
Code editors that read your files have a structural problem with the frontend: they cannot see it. An agent can parse a component tree perfectly and still have no idea that a padding value pushes a heading off the screen at 375 pixels wide, because it has never looked at the screen. Frontend work is visual, and most agents are working blind.
stagewise's answer is to hand the agent the things a developer takes for granted. When you click an element, the toolbar collects the DOM node, a screenshot, and the surrounding browser context, then sends that package to the agent along with your comment. The model is no longer guessing what "here" means. It has the pixels.
02 - HOW IT WORKSPoint, comment, and let the agent do the typing
The mechanics are deliberately boring, which is a compliment. You run one command from your project root, stagewise proxies your dev app, and a toolbar appears inside the running interface. From there the loop is short.
Run it
Start with npx stagewise from your project root.
Click
Select the UI element you want to change, right in the live app.
Comment
Describe the change in plain language, like a code review note.
Ship
The agent edits your local source; you watch it update in place.
One line gets you started: npx stagewise - it proxies your dev app and injects the toolbar. No account required to look around.
03 - THE WEDGEA free toolbar that arrived before the company
Before stagewise was a company, it was a download. The open-source toolbar spread the way developer tools tend to when they scratch a real itch - quietly, by word of mouth, until the numbers stopped looking like a side project. More than 130,000 downloads and 4,800 GitHub stars accumulated around a thing that was free and had no signup wall.
That order matters. The audience existed first; the business arrived on top of it. It is a familiar move in developer tooling, and it works because trust is cheaper to earn when you are not asking for a credit card on the first screen.
04 - THE MOATBet on the browser, not on a framework
Plenty of tools tie themselves to one stack. stagewise made the wider bet: if it runs in a browser, it is fair game. React, Vue, Angular, and Next.js are supported, and so is vanilla JavaScript - and, in a detail that says a lot about the philosophy, Ruby on Rails ERB templates too. The common denominator is not a framework. It is the rendered page.
The company keeps the interface that connects agents open source, on GitHub at stagewise-io/stagewise. What it sells sits one layer up: the hosted agent that turns your comment into a correct edit, billed on credits, with a small free tier of roughly two euros to kick the tires on four or five real tasks.
05 - THE PEOPLEFrom embedded firmware to the browser
stagewise is the work of two founders, Glenn Toews and Julian Goetze, based in Bielefeld, Germany - a city best known, fittingly for a company obsessed with what is really on screen, for a long-running German joke about whether it exists at all. Toews, the CEO, came to frontend AI by an unlikely road: electrical engineering, then embedded software in automotive and premium appliances at names like Rheinmetall and Miele. Goetze, the CTO, had already shipped a product to 5,000 monthly users before this one.
Their stated ambition runs past the current tool. The near-term goal is to put developers in their users' shoes; the longer-term one is a world where production-grade user experience can be built quickly, eventually by people who do not code at all. It is a large claim from a two-person team, but it is a legible one.
06 - THE MARKETWhere it sits among Cursor, v0, and the rest
The field is crowded. Cursor rethinks the editor. v0 and Lovable generate UI from prompts. Bolt and Replit's agent spin up whole apps. stagewise is not trying to replace any of them at their own game. Its position is more specific: the place where a frontend change actually happens, inside the running app, on a codebase that already exists and already matters. For a developer who has moved past the prototype and is tired of the tab-switch between browser and editor, that specificity is the point.