An Agent That Ships.
Built on Kael, the same composite intelligence behind the API. Point it at a codebase and it plans, writes, and finishes the work — not just suggests it.
From Task To Shipped.
Describe the change. Harness reads the codebase, plans the change, writes it, and checks its own work before handing it back — the same draft-then-check discipline that makes Kael what it is, applied to your repo.
Watch A Task Become A Change.
A task goes in as plain language. Files change, the work is checked, and a report comes back with what was done.
It's Not Just An Agent. It's What The Agent Runs In.
Most coding agents are the whole product — you talk to them, they write code, that's the entire experience. Quan Harness is different: the agent is only one part of it. The harness is the environment that agent runs inside — the file system, the live preview, the deployment, the routing between specialized agents underneath. The agent does the work; the harness is what makes that work real, testable, and shippable, not just written.
A Real Project Environment, Not A Chat Window.
Many AI coding tools give you a conversation: you describe what you want, and they write code on a machine you run yourself. Harness gives you a project instead: a full file system scoped to what you're building, that you can browse and edit yourself with the built-in file editor, plus a live preview the moment something changes — so you're looking at the running thing, not just the code that's supposed to produce it.
Push and pull to GitHub the same way you would locally. And you're not boxed into one language or framework — build in whatever stack you're already comfortable with.
One Task, The Right Agent For It.
The agent side of Harness does more than write code — connect it to your other tools through MCP, give it skills for the specific things you need done, and it can act on all of it.
But it isn't one enormous agent trying to be everything at once. Ask it to check your inbox and draft replies, and that hands off to an agent built for exactly that — not the same one that's mid-way through refactoring your auth flow. Most tools route every request through a single, increasingly complicated system prompt; when something breaks, it's hard to know why, and harder to fix without breaking something else. Harness routes each kind of task to a purpose-built agent instead — more predictable for you, easier for us to improve without the whole system shifting under it.
Built To Be Right, Not Just Fast.
Precision, accuracy, and completeness come first here — speed second. Where other agents wait for you to ask "are there any bugs?", Harness flags what it notices along the way without being asked, as part of the work it's already doing, not a separate search for problems. You decide what to do with that — fix it now, later, or not at all — but you'll know about it either way.
That means a task might take a little longer than the fastest tool you've tried. It also means you're less likely to get back something that technically matches what you asked for but isn't actually good. And because everything runs in the cloud, you don't have to sit and watch it work — send the task, get on with your day, and get notified when it's done.
Everything In The Harness.
- Live preview
- The project is deployed instantly, so you test the running thing in the browser, not just the code.
- Your own language & framework
- Build in whatever stack you already use.
- Cloud file system
- A full file manager scoped to your project. Browse, edit and move things freely with the built-in editor.
- Git
- Push and pull to GitHub, just like local.
- MCP and skills
- Connect your other tools through MCP, and give the agent skills for the specific jobs you need done.
- An agent per task type
- Each kind of task is routed to a purpose-built agent, instead of one agent trying to do everything.
- Runs in the cloud
- Send the task and get on with your day. You are notified when it is done.
The Same System As The API.
Harness runs on Kael, so it shares Kael's character: accuracy over speed, strongest at code, security and multi-step engineering work. If you want the model without the agent around it, the same system is available as an API.
How Kael works →One subscription, unlimited use. See exact pricing on the app.