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If you want a Happo alternative that checks what a change did in the running app (requests, state, console), Reticle is built for that. If you want cross-browser and mobile visual diffs your agent can check over MCP, Happo is the stronger choice, and Reticle is not a pixel diff.
What Happo does
Happo captures Storybook stories, Playwright, Cypress or Vitest tests, renders them in Chrome, Firefox, Safari, Edge and iPhone and iPad Safari, diffs against the base and posts a PR status. Native iOS and Android screenshots can be uploaded too, and it includes accessibility diffs (happo.io).
It pitches the same agent loop we do, on pixels: "With Happo's MCP server, the agent checks its own work first, so the pull request it hands you is ready for review" (MCP docs). The MCP server is on every plan, including free.
Pricing is public: Free (5,000 snapshots, Chrome), Starter $149, Growth $399, Pro $749, Enterprise custom (pricing, checked 2026-10-25). The client is public; the rendering service is closed.
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.
Your agent calls it through MCP while it works. Flows it drives are saved and replay deterministically, with no model in the loop. It also drives sites you don't own, reading network, console and DOM there; app state and file:line need its SDK in your build. The SDK is open source (Apache-2.0); the hosted platform runs the same checks on previews and pull requests.
Happo vs Reticle at a glance
| Happo | Reticle | |
|---|---|---|
| What it checks | Screenshots across browsers and devices, plus accessibility diffs | Network, app state, console and DOM after each step |
| Browsers and devices | Chrome, Firefox, Safari, Edge, iOS Safari, native mobile uploads | Web, one engine |
| Agent integration | Remote MCP server, every plan | MCP tools the agent calls while it works |
| Pixels | Yes | No pixel diff; reads DOM and computed styles |
| Points to the fix | The changed snapshot | The failing request or state, and file:line on React and Svelte |
| Open source | Client only | SDK Apache-2.0; server FSL-1.1 |
| Pricing | Free; from $149 | Start free, no card; open-source SDK free |
Where Happo is the better choice
- You need real Safari, iOS and Edge rendering. Happo renders on those engines and accepts native mobile screenshots. Reticle runs on one web engine.
- You care about pixels and accessibility diffs. Reticle is not a pixel diff; in our benchmark a 2.3% CSS re-tint was caught by a screenshot and missed by Reticle (scorecard).
- You want an agent self-check on visuals today, on a free plan. Happo's MCP server is already on every plan.
- Your coverage lives in Storybook. Every story becomes a cross-browser snapshot.
Where Reticle is the better choice
- The bug is not visible. A payment request sent twice, a write that returns 200 and never lands, a console error under a working page. Reticle reads those directly, so the step fails while every screenshot matches.
- You need the fix location, not only the symptom. The verdict names the failing request or state and, on React and Svelte, the source line.
- You want whole flows across the backend. Reticle drives sign-up, checkout or refunds in the running app against your real dev or preview backend.
- You want deterministic re-runs. Saved flows replay with no model in the loop: eight replays, one verdict.
On 88 seeded bugs, Reticle caught 85 with no false alarms; two of the other three are traps a correct tool must not flag, and one is a genuine miss. The method is in the benchmark scorecard.
Can you use both?
Yes. Happo lets the agent check that the UI looks right on every engine; Reticle lets it check that the change behaves right. Both work over MCP, so one agent session can call both.
See why a green check isn't proof, and the Argos alternative and Percy alternative pages for other visual tools.
Try Reticle in five minutes
Paste one line to your coding agent, and it installs and wires the SDK in your app:
Follow https://raw.githubusercontent.com/reticlehq/reticle/main/SKILL.md
Or run npx @reticlehq/core init yourself. The README has the details.
FAQ
What is the best alternative to Happo?
The best alternative to Happo depends on what you need checked. For other cross-browser visual diffs, look at Percy, Chromatic, Argos or Applitools. For checking that an agent's change worked in the running app, through network, state and console with the source line to fix, Reticle fits. Pixels and behaviour are separate checks.
Does Happo have an MCP server?
Yes, Happo has a remote MCP server on every plan, including free. It lets coding agents such as Claude Code and Cursor list comparisons, read diffs and accept or reject them. Reticle also has MCP tools, but they check network, state and console in the running app rather than screenshots.
How is Reticle different from Happo?
Reticle is different from Happo in what it compares. Happo renders screenshots across browsers and devices and diffs them against a base. Reticle runs the flow in the app and reads requests, state and console after each step, so it catches failures that look identical, but it does not diff pixels.
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.