Sentry Seer's AI code review predicts the errors a pull request is likely to cause, using the runtime context Sentry already collects about your application. Design Bug Bot reviews a different layer of the same pull request: whether new React UI reuses your existing components, stays on your spacing and type scale, and still works at mobile width.
The overlap is small, partly because Sentry says its review leaves out style feedback. Use Seer to catch code that will break in production; add Design Bug Bot when your frontend review comments are about consistency and layout rather than crashes.
Disclosure: This comparison is published by 21st, which makes Design Bug Bot. It is based on official documentation for both products, checked on September 14, 2026. It is not a head-to-head benchmark: we have not run a common benchmark, and nothing below reports test results.
Seer code review and Design Bug Bot at a glance
| Sentry Seer code review | Design Bug Bot | |
|---|---|---|
| Review job | Predicts errors in a change and makes suggestions before merge. Seer code review docs | Reviews changed UI code for consistency, layout risks and unnecessary dependencies. |
| Evidence it uses | Runtime context, such as behavior under heavy traffic and requests that caused related problems. Seer AI code review | Your repository's existing components, tokens, spacing and type scale. |
| Style and design feedback | Left out on purpose: Sentry says the review skips style and best-practice nits. Seer AI code review | The core job: duplicate components, off-scale styles, overflow, hidden mobile actions. |
| Rendered UI | Not described in the docs we checked. | Screenshots and visual checks at desktop and mobile widths when an isolated render succeeds. |
| When it runs | Ready-for-review pull requests, each later commit, or a "@sentry review" comment. Seer code review docs | Pull request updates, plus default-branch reviews run manually, after a set number of commits, or on a schedule. |
| Merge gating | A status check you can add to branch protection; Sentry recommends keeping it optional. Seer code review docs | Advisory: one updated comment and a GitHub check per reviewed commit. |
| Git hosts | GitHub and GitLab.com; self-hosted instances are not supported. Seer code review docs | GitHub. |
| Pricing model | Add-on priced per active contributor. Sentry pricing docs | Five free successful reviews, then AI credits. Details |
What Seer adds to a pull request
A reviewer that reads only source code has to guess how a change will behave under real traffic. Seer's review uses what Sentry has already observed: how your code behaves under heavy load, what happens when services interact, and which requests, services and events caused related problems before. Seer AI code review
The scope is narrow on purpose. Sentry positions the review around the most impactful errors a change could cause and avoids style and best-practice comments. It also belongs to the wider Seer agent, which works from issue details, stack traces, traces, logs and profiles, and whose Autofix feature finds root causes and can open pull requests. Seer overview
Gating is conservative. Reviews start when a pull request is ready for review, skip drafts, and can be requested by commenting "@sentry review". You can add the status check to branch protection, but the docs recommend keeping it optional. Seer code review docs
The UI problems Seer leaves to someone else
Picture a pull request that adds a pricing card. Nothing in it throws, and no trace gets slower. An error-focused review has little to say, and that is by design.
A frontend reviewer would still flag three things: the card builds its own button instead of using the shared one, its heading uses a size that is not on your type scale, and a fixed width makes the page scroll sideways on a phone. None of these create a Sentry event.
Design Bug Bot is built for that pull request. It reviews changed UI code against the components, tokens, spacing and type scale already in your repository, and looks for horizontal overflow, fixed widths and actions hidden on mobile. It also flags unnecessary dependencies, and its performance findings require measurements rather than guesses.
Each finding explains the problem, points to the file and line when available, and includes suggested fix code you can inspect, copy or hand to a coding agent. Changed pages and components are rendered in a React harness inside a disposable sandbox; when the render succeeds, the review can include screenshots at desktop and mobile widths. When it cannot render, you still get code-backed recommendations without screenshots.
The limits run the other way too. Design Bug Bot has no production telemetry and is not a general reviewer for logic, security or backend bugs, so it will not warn you about an unhandled error in your API route. It works on GitHub, with React codebases.
Using both on one frontend team
A checkout change that touches both layers. The pull request changes the payment request and redesigns the form. Seer's runtime context is the relevant check for the request path; Design Bug Bot checks that the form reuses your inputs and fits a phone screen.
A settings page restyle. Nothing is likely to fail at runtime, so the useful questions are spacing, type sizes, and whether a new toggle duplicates one you already have. That is Design Bug Bot's territory.
A repository on GitLab.com. Seer's docs list GitLab.com support. Design Bug Bot is GitHub only, so the pairing is not available there.
Seer pricing
Seer is listed at $40 per active contributor per month, as an add-on for Sentry Team and Business plans, listed on Sentry's pricing docs on September 14, 2026. An active contributor is anyone who makes two or more pull requests to a Seer-enabled repository in a month.
Design Bug Bot gives new accounts five successful reviews free, with no subscription required. After that, reviews need a subscription that includes AI and draw AI credits from the same balance as 21st AI. See the trial and billing details.
Try the pair on your own history
- Pick two merged pull requests: one that later caused a Sentry issue, and one that later needed a UI follow-up, such as swapping a custom control for the shared one. Recreate each on a branch from the commit before the fix.
- Record the evidence. For Seer, note whether a finding refers to production behavior. For Design Bug Bot, note whether it names the existing component or token and whether a mobile screenshot was available.
- Add two out-of-scope changes. A backend-only pull request and a pure restyle show how each review handles work outside its job. Design Bug Bot gives a pull request with no UI files a neutral check and no comment.
- Price your volume. Count the people who open two or more pull requests a month in the repositories you would enable, and set that against the UI reviews you expect.
For what to check by hand, see the React UI code review checklist; for a general code reviewer paired with the same design pass, read CodeRabbit vs Design Bug Bot.
Frequently asked
- Does Sentry Seer comment on code style?
- No, by design. Sentry's AI code review page says the review skips nits about style and best practices and focuses on the errors a change is likely to cause. Design consistency is the gap Design Bug Bot is built to review.
- What context does Seer use that a code-only reviewer lacks?
- Seer draws on what Sentry has observed in production, such as how code behaves under heavy traffic and which requests and services caused related problems. Design Bug Bot has no production telemetry; its reference is your repository's components and styles.
- Will either tool block my merge?
- Seer posts a status check you can add to branch protection, though Sentry's docs recommend keeping it optional. Design Bug Bot is advisory: it updates one review comment and posts a GitHub check per reviewed commit without blocking merges.
- How much does Seer cost?
- On September 14, 2026, Sentry's pricing docs listed Seer at $40 per active contributor per month, as an add-on for Team and Business plans. An active contributor makes two or more pull requests to a Seer-enabled repository in a month.