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Reticle is a verification layer for AI coding agents. It embeds a dev-only SDK inside your running web application and exposes what that application is actually doing, its DOM, network calls, routing, console, and framework state, as structured tools an agent can call over MCP. The agent names the consequence it expects, performs an action, and gets back a verdict: pass, fail, or an honest “couldn’t tell”, with the evidence and the file:line to open. It exists because an agent that writes code cannot otherwise tell whether that code works. Reading the diff proves nothing. Unit tests do not run the application. A screenshot shows a page that renders perfectly over a failed request.

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How it works, in three parts

  1. An SDK inside the app. Dev-only, stripped from production builds, added by a build plugin. It instruments the DOM, network, routing, console, animations, and your state library.
  2. A local bridge. The SDK connects over a WebSocket to a daemon on your machine. Reticle never starts or manages your dev server; it attaches to the app you are already running.
  3. An MCP server. The daemon exposes the app to your agent as tools. reticle_snapshot to look, reticle_act_and_wait to act and prove in one call, reticle_state and reticle_network to observe, reticle_assert to check.
Everything stays on your machine. No application code, DOM, network traffic, or console output leaves it.

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What Reticle is not

This is the section most people need, because Reticle sits next to several familiar categories without being any of them. Not a browser automation framework. Playwright, Cypress and Selenium drive a browser from the outside and are excellent at it. Reticle runs inside the page you already have open. If you want to script a browser, use Playwright. Reticle is what an agent uses to answer “did the thing I just changed actually work?” Not a replacement for your test suite. Unit and integration tests still do their job. Reticle covers the layer they structurally cannot reach: behaviour that only exists when the whole application runs. Many teams use both, and Reticle is often the thing that catches a suite passing over a broken app. Not a screenshot or visual regression tool. It can take screenshots, but the point is that it does not need to. Verdicts come from predicates over real events, a request with a status, a state path, a signal your code fired, so they do not break when a button moves four pixels. If pixel-perfect visual diffing is your goal, a dedicated visual testing service fits better. Not a monitoring or observability product. Reticle is a development-time tool aimed at localhost. It is not an APM, not error tracking, and it does not watch production. Not an accessibility auditor. reticle_snapshot addresses elements by role and name, which is not the same as auditing contrast, focus order, or screen reader behaviour. Use a dedicated accessibility tool for that. Not an AI model, and not an agent. Reticle has no model of its own and makes no decisions. It gives an agent you already use a way to see the running app. Your agent, your model, your keys. Not a hosted service that receives your application data. The daemon runs on your machine and the SDK runs in your browser. Anonymous product analytics are sent unless you opt out, and they never include your code or your application’s data. See the Telemetry Policy. Not a way to make a failing check pass. A verdict of unknown means Reticle drove the app and could not tell. It is deliberately not rounded up to a pass, because a verification tool that flatters you is worse than none.

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What Reticle needs

Honest constraints, so you can tell in a minute whether it fits:
  • A web application you can run locally, with its dev server. Reticle attaches; it does not start one.
  • A build step it can hook, or two lines added by hand. Vite, Next.js, Remix and Astro are proven by gates in the repository. The SDK is framework agnostic and usually connects elsewhere, with reduced source mapping.
  • An agent that speaks MCP. Claude Code, Cursor, Codex, Copilot, Windsurf, OpenCode and others.
  • Node 20 or newer.
Electron and Tauri desktop applications are supported, including the IPC boundary a browser-based tool cannot observe at all.

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How it compares

Side by side with the tools people ask about most:

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Where to go next

  • Quickstart gets a real verdict out of your own app in about five minutes.
  • Why Reticle is the argument, with the evidence and the cases where it loses.
  • For agents is written for the agent rather than for you.
Last modified on August 15, 2026