docs/src/content/en/guides/guide/code-review-bot.mdx
import Steps from "@site/src/components/Steps"; import StepItem from "@site/src/components/StepItem";
In this guide, you'll build a code review bot that automatically reviews pull requests using workspace skills. The bot loads coding standards from skill files and provides structured feedback. You'll learn how to create a workspace with a skills directory, define an Agent Skill with review instructions and reference files, and connect it to an agent that performs automated reviews.
v22.13.0 or later installedIn your src/mastra/index.ts file, import the Workspace and LocalFilesystem classes. On the Workspace instance, configure the skills option to point to a skills directory. The skills directory will live inside the filesystem's basePath.
import { Mastra } from '@mastra/core'
// highlight-start
import { resolve } from 'node:path'
import { Workspace, LocalFilesystem } from '@mastra/core/workspace'
// highlight-end
// highlight-start
const workspace = new Workspace({
filesystem: new LocalFilesystem({
basePath: resolve(import.meta.dirname, '../../workspace'),
}),
skills: ['/skills'],
})
// highlight-end
export const mastra = new Mastra({
// highlight-next-line
workspace,
})
At the root of your project, create a new folder called workspace. Inside that, create a skills folder. This is where you'll define the code standards skill in the next step.
Skills are structured directories containing a SKILL.md file with instructions for the agent. The code standards skill defines the review process and references a style guide.
Inside workspace/skills, create a new folder called code-standards. Create a file called SKILL.md and add the review instructions.
---
name: code-standards
description: Automated code review standards and checks
---
# Code Review Standards
Review code systematically using these steps:
1. **Critical Issues**: Security vulnerabilities, memory leaks, logic bugs, missing error handling
2. **Code Quality**: Functions over 50 lines, code duplication, confusing names, missing types
3. **Style Guide**: Check references/style-guide.md for naming and organization
4. **Linting**: Flag common issues like use of `var`, leftover `console.log` statements, and `debugger` statements
Provide feedback in this format:
**Summary**: One sentence overview
**Critical Issues**: List with line numbers
**Suggestions**: Improvements that would help
**Positive Notes**: What the code does well
Inside workspace/skills/code-standards, create a references folder to hold reference materials for the skill. Author a style guide file that outlines the project's coding conventions with the file name style-guide.md.
# Style Guide
## Naming
- Variables/Functions: `camelCase`
- Constants: `UPPER_SNAKE_CASE`
- Files: `kebab-case.ts`
- Booleans: Start with `is`, `has`, `should`
## Code organization
```typescript
// 1. Imports
import { foo } from 'bar'
// 2. Constants
const MAX_SIZE = 100
// 3. Types
interface User {
id: string
}
// 4. Functions
function doSomething() {}
// 5. Exports
export { doSomething }
```
## Error handling
Always handle errors explicitly - never silently catch.
## Comments
Write "why" not "what".
Now it's time to create the code review bot agent that uses the code-standards skill. Create a new file at src/mastra/agents/code-reviewer.ts and define the agent:
import { Agent } from '@mastra/core/agent'
export const codeReviewer = new Agent({
id: 'code-reviewer',
name: 'Code Review Bot',
instructions: `You are an automated code reviewer.
When asked to review code:
1. Activate the 'code-standards' skill
2. Follow the review process from the skill
3. Check against the style guide in skill references
4. Be constructive and specific with line numbers`,
model: 'openai/gpt-5.4',
})
Define the agent by importing it inside src/mastra/index.ts and registering it with the Mastra instance:
import { Mastra } from '@mastra/core'
import { resolve } from 'node:path'
import { Workspace, LocalFilesystem } from '@mastra/core/workspace'
// highlight-next-line
import { codeReviewer } from './agents/code-reviewer'
const workspace = new Workspace({
filesystem: new LocalFilesystem({
basePath: resolve(import.meta.dirname, '../../workspace'),
}),
skills: ['/skills'],
})
export const mastra = new Mastra({
workspace,
// highlight-next-line
agents: { codeReviewer },
})
Start Mastra Studio and interact with the code review bot to see it in action.
npm run dev
Open localhost:4111 and navigate to the code reviewer agent.
Inside the chat input, provide a code snippet for review, such as:
Review this code:
function getData(id) {
var result = fetch('/api/data/' + id);
console.log(result);
return result;
}
The bot should activate the code-standards skill and provide structured feedback. Since agent responses are non-deterministic, your output may vary, but you should see something similar to:
**Summary**: Function has several issues with variable declaration,
debugging statements, and missing error handling.
**Critical Issues**:
- Missing error handling for fetch (line 2)
- No async/await for asynchronous operation (line 2)
**Suggestions**:
- Use const instead of var (line 2)
- Remove console.log before committing (line 3)
- Add TypeScript type for id parameter
- Use template literals instead of concatenation
**Positive Notes**:
- Function name is clear and descriptive
You can extend this bot to:
Learn more: