Tencil

Tencil is an open-source browser review tool for coding agents, published under the Apache-2.0 license and operated under the trade name of Pixel Perfect. Press C on a running dev site, click an element and describe what should change. Tencil hands the agent the element's component, source file and markup, then streams progress back onto the pin while the dev server hot-reloads.

What It Is

Tencil is a point-and-prompt layer between your running app and a coding agent. Instead of explaining where something lives in the code, you select the element on the page. The prompt goes to a new agent thread, or to a thread the agent already worked in, along with the element's component, source file and markup, plus a screenshot if you attach one.

The project's README likens it to Vercel Comments, except the reviewer on the other side is an agent.

How the Workflow Runs

Running npx tencil detects Next.js or Vite, shows the diff and asks before changing files. It adds <Tencil /> to a Next.js root layout or tencil() to Vite plugins, and any other dev server uses one script tag. You can queue comments across a page and send them all to your agent. Threads open next to the page so you can read the agent's work and reply for another round.

Local-First Architecture

A single daemon per machine serves the overlay on localhost and talks to the agent. The site states there is no Tencil server and no account, and no telemetry. The overlay loads only in development, so production builds leave it out. The daemon accepts only loopback origins unless --allow-origin is passed. Pins are stored per project under ~/.config/tencil/projects/.

Agents and Frameworks

The site lists T3 Code and Claude Code as supported agents, and the README also documents an Ensemble provider. Next.js (app and pages router) and every Vite app are supported, and React apps get component and source file detection. Setup requires Node 22 or newer, and the agent runs under your own login.