# Yo Bug

> MCP Server that gives AI coding assistants QA testing capabilities — point at bugs, AI fixes them

- **Type:** MCP server
- **Install:** `agentstack add mcp-wyykerwin-yo-bug`
- **Verified:** Yes — security-reviewed for prompt injection and unsafe behavior
- **Seller:** [WYYkerwin](https://agentstack.voostack.com/s/wyykerwin)
- **Installs:** 0
- **Category:** [Web & Browser](https://agentstack.voostack.com/c/web-and-browser)
- **Latest version:** 0.1.0
- **License:** MIT
- **Upstream author:** [WYYkerwin](https://github.com/WYYkerwin)
- **Source:** https://github.com/WYYkerwin/yo-bug

## Install

```sh
agentstack add mcp-wyykerwin-yo-bug
```

Requires the [AgentStack CLI](https://agentstack.voostack.com/docs/cli). Works with Claude Code, Cursor, and any MCP-compatible agent.

## About

# yo-bug 🐛

**English** · [简体中文](./README.zh-CN.md)

**"Yo, bug!"** — Point at bugs, AI fixes them.

MCP Server that gives AI coding assistants QA superpowers. One install, then your AI handles the entire test-feedback-fix loop.

In vibe coding, the bottleneck is testing: humans find bugs but struggle to describe them. yo-bug solves this by letting users point, click, or type — while the AI automatically receives element locations, console errors, network failures, action recordings, and annotated screenshots.

## What it does

| For the Human | For the AI |
|---|---|
| Click a broken element → done | Gets: CSS selector + computed styles + React/Vue component name |
| Draw on a screenshot → done | Gets: annotated PNG as inline image content |
| Type a behavior bug ("scroll doesn't auto-jump") → done | Gets: structured text feedback linked to a checklist case |
| Check off a multi-step test case | Gets: which cases passed/failed, with linked feedback per case |
| Just use the app normally | Gets: last 100 user actions + 50 console errors + failed network calls |

The AI drives the entire workflow through MCP tools. Humans never need to learn commands, configure proxies, or modify their code.

## Install

```bash
npx yo-bug install
```

(or `npm install -g yo-bug && yo-bug install` if you prefer a global install)

This auto-detects your AI tool (Claude Code / Cursor / Windsurf) and writes the MCP config. One time, done forever.

## How it works

```
AI writes code
    → AI calls start_test_session()
    → Reverse proxy starts, injects test SDK into HTML responses
    → Browser opens (zero code changes to your project)
    → AI pushes grouped test cases (8 QA dimensions, multi-step scenarios)
    → Human runs each case; pass/fail at the case level
    → When failing, picks feedback mode: element / screenshot / text
    → AI calls list_feedbacks() + get_feedback() — sees diagnostic data
    → AI must state root cause BEFORE writing fix (enforced by tool response)
    → AI fixes → calls resolve_feedback() → browser shows verify card
    → Human clicks Fixed / Locate (jump to element) / Still broken
    → Loop until done
```

## MCP Tools (9 total)

### Session Control
| Tool | Description |
|---|---|
| `start_test_session(port?, open?, storage?)` | Start test mode: auto-detect dev server, launch reverse proxy with SDK injection, open browser. `storage` defaults to `"project"` (saves under `/.yo-bug/feedback/`); pass `"home"` for `~/.yo-bug/` |
| `stop_test_session()` | Stop test mode, return session summary (feedback stats, checklist results, weak dimensions, whether dev server was auto-closed) |

### Feedback
| Tool | Description |
|---|---|
| `list_feedbacks(status?, type?, limit?, all_sessions?)` | List submitted feedback. Defaults to current session only |
| `get_feedback(id)` | Full details: element info, console errors, network errors, action steps, annotated screenshot. Response includes a **mandatory diagnostic protocol** that forces the AI to identify root cause before writing code |
| `resolve_feedback(id)` | Mark as fixed → pushes a rich verification card to the browser (with screenshot thumbnail, element selector, page URL, locate button). Human confirms |

### Test Checklist (Grouped Test Cases)
| Tool | Description |
|---|---|
| `create_checklist(title, cases)` | Push structured test cases to browser. Each case has a title, sequential `steps[]`, expected result, priority, and QA dimension |
| `get_checklist_status()` | See which cases passed/failed and any user feedback per case |

### Test History
| Tool | Description |
|---|---|
| `save_test_record(module, ...)` | Save test results per module. Accumulates history for future reference |
| `get_test_history(module)` | Get historical test records. Shows frequently failing scenarios so AI prioritizes coverage |

## 8 QA Test Dimensions

The `create_checklist` tool embeds professional QA methodology. AI is guided to cover:

1. **Happy path** — Core functionality works end-to-end
2. **Empty/boundary** — Empty inputs, special chars, max length, zero/negative values
3. **Error states** — Offline, server errors, timeouts, recovery
4. **Duplicate ops** — Double-click, re-submit, concurrent requests
5. **State recovery** — Refresh, back/forward, deep links, tab close/reopen
6. **Loading/async** — Loading states, failed loads, stale data
7. **Responsive** — 375px mobile width, touch targets, overflow
8. **Interaction detail** — Tab order, Enter/Escape, disabled states, focus

Each case is multi-step (open page → fill form → click submit → verify result), so the human marks a whole scenario passed/failed rather than micro-managing each step.

## Three Feedback Modes

When a checklist case fails, users pick a mode that fits the bug:

| Mode | Shortcut | When to use |
|---|---|---|
| **Element** | `Alt+E` | Visual / component bug — click the broken element, AI gets selector + styles + framework component name |
| **Screenshot** | `Alt+S` | Layout / styling bug — drag to select a region, annotate with arrow / rect / circle / freehand / text |
| **Text** | (Checklist `✗`) | Behavior / logic bug ("doesn't auto-scroll", "wrong order") — pure description, AI uses console/network data to find cause |

Other shortcuts: `Alt+X` toggle mode bar, `Esc` exit anything.

## In-Browser Feedback Management

Above the floating bug button you'll see a list icon with a red badge showing open feedback count. Click it to:

- See all open feedback you've submitted this session
- Edit description inline (click description text)
- Delete a feedback (trash icon, confirms first)
- View screenshot thumbnails

When all feedback is resolved, the button auto-hides.

## Auto-Captured Context

Every feedback submission automatically includes:

- **Console errors** — last 50 `console.error`/`console.warn` entries with stack traces
- **Network failures** — last 50 failed `fetch`/`XHR` requests with status, URL, duration
- **Unhandled exceptions** — last 50 `window.onerror` + `unhandledrejection` events
- **Action recording** — last 100 user actions (click / input / navigate / scroll / keypress) with timestamps
- **Element info** — CSS selector, tag, text content, bounding rect, computed styles, React/Vue component name (when in element mode)

## Verify-Fix Flow

When AI calls `resolve_feedback()`, a rich verify card appears on the left:

```
┌─────────────────────────────┐
│ ▼ VERIFY FIX            [3] │  ← collapsible header with count
├─────────────────────────────┤
│ [thumbnail*] "Button click  │
│              does nothing"   │
│              bug · element   │
│  📍  #submit-btn    │  ← only when element info exists
│  🔗 /orders                  │
│  ⏱ 5 min ago                │
│  [🎯 Locate*] [✓] [✗]        │
└─────────────────────────────┘
   * thumbnail only if a screenshot was attached
   * Locate only if an element selector was captured
```

- **🎯 Locate** scrolls to the element + flashes a red pulse twice. If the verify card was submitted on a different URL, it navigates there first. If the element no longer exists on the current page, shows a toast
- **✓ Fixed** confirms the fix → status: resolved
- **✗ Still broken** sends it back → status: open (AI sees it in next `list_feedbacks` call)
- Click the header bar to collapse the whole stack when it gets in the way

## Theming

- Auto-detects `prefers-color-scheme` (light or dark)
- All UI uses design tokens, contrast-verified (WCAG AA)
- Glass-morphism panels with backdrop blur; clearly distinct from white host pages

## Works Inside Modal Dialogs

If your app opens a `.showModal()` (which traps focus and inerts the rest of the page), yo-bug still works: it detects the open modal via the `:modal` selector plus a `MutationObserver`, and relocates the SDK host inside the dialog so focus is shared.

This means you can submit text feedback even when a modal is open — the textarea will accept input normally. When the dialog closes, the host moves back out.

## i18n

SDK auto-detects ``:
- Any value starting with `zh` (`zh`, `zh-CN`, `zh-Hans`, ...) → Chinese interface
- Everything else → English interface

MCP tool descriptions are in English (AI translates to the user's language naturally in chat).

## Architecture

```
Browser → Reverse Proxy (localhost:3695+) → Dev Server (localhost:5173)
              │
              ├─ Auto-injects SDK into HTML responses
              ├─ WebSocket passthrough (HMR works normally)
              ├─ Feedback API (POST/GET/PATCH/DELETE)
              ├─ Checklist API (push/poll/update)
              └─ Verify API (push/confirm)

MCP Server (stdio) ← AI Tool (Claude Code / Cursor / Windsurf)
              │
              ├─ start/stop_test_session → controls proxy lifecycle
              ├─ feedback tools → reads user submissions w/ diagnostic protocol
              ├─ checklist tools → pushes grouped test cases, reads results
              └─ history tools → persists test records per module
```

The proxy auto-detects dev server framework (Vite, Next.js, CRA, Webpack, Nuxt, Angular, Svelte, Astro) and port. If the dev server is already running, it connects. If not, it starts one. On `stop_test_session` it cleans up — and tells the AI whether the dev server was auto-closed or left running (because the user had started it themselves).

If port `3695` is taken, yo-bug auto-increments to `3696`, `3697`... up to `3795`. Multiple projects can run yo-bug simultaneously without conflict.

## Security

- All data stays local — feedback files in `/.yo-bug/feedback/` by default (auto-`.gitignore`'d), or `~/.yo-bug/` if you opt in
- Feedback IDs validated against path traversal
- Input fields whitelist-filtered and length-limited
- Network interceptor uses exact pathname matching (no substring false positives)
- No data sent to any external service

## Requirements

- Node.js >= 18
- Any MCP-compatible AI tool
- A current-version browser (Chrome / Edge / Firefox / Safari)

## License

MIT

## Source & license

This open-source MCP server is cataloged on AgentStack and links to its original source — we do not rehost the code.

- **Author:** [WYYkerwin](https://github.com/WYYkerwin)
- **Source:** [WYYkerwin/yo-bug](https://github.com/WYYkerwin/yo-bug)
- **License:** MIT

Install and usage instructions live in the source repository linked above.

## Pricing

- **Free** — Free

## Security capabilities

Automated source analysis of v0.1.0 — what this tool can access:

- **Network access:** yes
- **Filesystem access:** yes
- **Shell / process execution:** no
- **Environment & secrets:** no
- **Dynamic code execution:** no

*"Yes" means the capability is present in the source — more access means more to trust, not that it is unsafe.*


## Versions

- **0.1.0** — security scan: passed — Imported from the upstream source.

## Links

- Listing page: https://agentstack.voostack.com/l/mcp-wyykerwin-yo-bug
- Seller: https://agentstack.voostack.com/s/wyykerwin
- Browse the marketplace: https://agentstack.voostack.com/browse

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Listed on AgentStack — the marketplace for AI agent skills and MCP servers. Every listing is security-reviewed. Creators keep 70%.