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If you want a Codex browser alternative because you work in the Codex CLI, where the built-in browser is not available, or because "it looked right" is not a test, Reticle adds a verdict from network, app state and console that replays with no model. If you use the Codex desktop app and want the agent to open and click your app with no setup, its built-in browser is the default.
What the Codex browser does
OpenAI describes it this way: "Browser lets ChatGPT open websites, gather current information, and take action while you stay in control" (docs). It launched with the Codex app update of 2026-04-16 (announcement).
In the ChatGPT and Codex desktop app it opens pages, including localhost, clicks, types and takes screenshots. An optional Developer mode uses full CDP to read console, network, DOM and styles, and an annotation mode lets you comment on elements. A Codex for Chrome extension works in your real Chrome. It uses a separate profile with no shared signed-in sessions, cannot automate file uploads, and asks per site before CDP access. Per the docs, the browser is not available in the Codex CLI or IDE extension. Codex is included in every ChatGPT plan, from Free to Enterprise (pricing).
What Reticle does
Reticle checks an AI coding agent's change from inside the running web app and returns a verdict with evidence. It reads the network calls, the application state and the console, and on React and Svelte it names the file:line to fix.
Codex calls it through MCP, from the CLI as well as the app. Flows it drives are saved and replay deterministically, with no model in the loop. It also works on sites you don't own: it drives the page in its own browser and injects its SDK, reading network, console, DOM and routing; app state and file:line need the SDK in your own build. The SDK is open source (Apache-2.0).
Codex browser vs Reticle at a glance
| Codex browser | Reticle | |
|---|---|---|
| Where it runs | Codex desktop app (and Codex for Chrome) | Any MCP agent, including the Codex CLI, plus CI |
| What it gives the agent | A browser; console and network in Developer mode | A verdict: pass, fail or cannot tell, with evidence |
| Who decides it worked | The model | A declared expected outcome, checked after the step settles |
| App state (store) | Not read | Read (with the SDK in your build) |
| Re-running a check | The agent drives it again | Deterministic replay, 0% flake over 8 replays |
| Pricing | Included in ChatGPT plans | Open-source SDK free; platform starts free |
Where the Codex browser is the better choice
- It is already there. Every ChatGPT plan includes Codex and the app's browser.
- Annotating the page. Commenting on elements for the agent is a design workflow Reticle does not offer.
- Protocol-level reads on demand. Developer mode exposes console, network, DOM and styles over CDP.
- Browsing beyond your app. Gathering information from other sites is part of what it does.
Where Reticle is the better choice
- You work in the Codex CLI or CI. The browser is app-only; Reticle runs from the CLI through MCP and from CI with
npx @reticlehq/server verify. - The failure is under the screen. Request counts, store values and console errors are checked against the step's expected outcome, so a correct-looking page with a wrong request fails.
- Re-runs cost almost nothing. About 480 tokens to re-verify four flows, about 251 times less than a model re-drive.
On 88 seeded bugs, Reticle caught 85 with no false alarms (scorecard).
Can you use both?
Yes. Use the Codex app's browser when you want to look and annotate; use Reticle for the pass or fail the agent must reach before it says done, and for the check that runs again on the next change. Setup is on the Codex testing page, and the Codex sandbox details are in Claude Code and Codex for testing.
Try Reticle
Paste one line to Codex, and it installs and wires the SDK in your app:
Follow https://raw.githubusercontent.com/reticlehq/reticle/main/SKILL.md
FAQ
Can Codex test my web app in a browser?
Yes. Codex can test your web app in the built-in browser of the Codex desktop app, which opens localhost, clicks, types and takes screenshots, with console and network in Developer mode. Per OpenAI's docs the browser is not available in the Codex CLI or IDE extension, so CLI users need an MCP tool instead.
What is an alternative to the Codex browser?
An alternative to the Codex browser is Reticle, which Codex calls through MCP from the CLI or the app. It checks network, app state and console against the step's expected outcome and returns pass or fail with evidence, then replays saved flows with no model. Playwright MCP is another option for driving a browser.
Does Reticle work with the Codex CLI?
Yes. Reticle works with the Codex CLI through MCP: add it with codex mcp add or in ~/.codex/config.toml, or paste the SKILL.md line and let Codex wire it. Codex then calls Reticle while it works and reads the verdict before reporting the change as done, with no desktop app required.
Why Reticle
Your agent says it works. Reticle checks.
- Checks each change inside the running app: network, state and console, not a screenshot.
- Returns a pass or fail with the evidence and the file:line to fix.
- Open-source SDK on your machine, or the platform on every preview and PR.
No credit card required.