Ultracite for Jules

Use Ultracite with Jules when you want a background coding agent to start from explicit repo standards instead of ad hoc prompts. It fits teams that queue work for async execution and still want predictable code shape when the result comes back.

Setup details

These values come from the same data Ultracite uses when it creates or updates Jules instructions, so the page matches what actually gets written into the repo.

AGENTS.md

Run npx ultracite@latest init --agents jules and Ultracite will update this file for the default setup.

Configuration file

Ultracite writes to this exact file when you initialize or update the agent integration.

Write mode

Append to existing instructions

Existing instructions stay in place and Ultracite appends its rules where the agent expects them.

Header handling

Writes rules directly

The generated file starts directly with Ultracite rules and skips an extra heading block.

Hook support

No separate hook file

Jules does not use a separate hook configuration in Ultracite.

Files Ultracite writes for Jules

This preview shows the exact default file content Ultracite writes for Jules when you use the standard Biome setup.

If Jules supports hooks, the second tab shows the companion hook config that runs after AI-driven edits.

Markdown AGENTS.md

# Ultracite Code Standards
This project uses **Ultracite**, a zero-config preset that enforces strict code quality standards through automated formatting and linting.

## Quick Reference
- **Format code**: `npx ultracite fix`
- **Check for issues**: `npx ultracite check`
- **Diagnose setup**: `npx ultracite doctor`

Biome (the underlying engine) provides robust linting and formatting. Most issues are automatically fixable.

---

## Core Principles
Write code that is **accessible, performant, type-safe, and maintainable**. Focus on clarity and explicit intent over brevity.

### Type Safety & Explicitness
- Use explicit types for function parameters and return values when they enhance clarity
- Prefer `unknown` over `any` when the type is genuinely unknown
- Use const assertions (`as const`) for immutable values and literal types
- Leverage TypeScript's type narrowing instead of type assertions
- Use meaningful variable names instead of magic numbers - extract constants with descriptive names

### Modern JavaScript/TypeScript
- Use arrow functions for callbacks and short functions
- Prefer `for...of` loops over `.forEach()` and indexed `for` loops
- Use optional chaining (`?.`) and nullish coalescing (`??`) for safer property access
- Prefer template literals over string concatenation
- Use destructuring for object and array assignments
- Use `const` by default, `let` only when reassignment is needed, never `var`

### Async & Promises
- Always `await` promises in async functions - don't forget to use the return value
- Use `async/await` syntax instead of promise chains for better readability
- Handle errors appropriately in async code with try-catch blocks
- Don't use async functions as Promise executors

### React & JSX
- Use function components over class components
- Call hooks at the top level only, never conditionally
- Specify all dependencies in hook dependency arrays correctly
- Use the `key` prop for elements in iterables (prefer unique IDs over array indices)
- Nest children between opening and closing tags instead of passing as props
- Don't define components inside other components
- Use semantic HTML and ARIA attributes for accessibility:
   - Provide meaningful alt text for images  
   - Use proper heading hierarchy  
   - Add labels for form inputs  
   - Include keyboard event handlers alongside mouse events  
   - Use semantic elements (`<button>`, `<nav>`, etc.) instead of divs with roles

### Error Handling & Debugging
- Remove `console.log`, `debugger`, and `alert` statements from production code
- Throw `Error` objects with descriptive messages, not strings or other values
- Use `try-catch` blocks meaningfully - don't catch errors just to rethrow them
- Prefer early returns over nested conditionals for error cases

### Code Organization
- Keep functions focused and under reasonable cognitive complexity limits
- Extract complex conditions into well-named boolean variables
- Use early returns to reduce nesting
- Prefer simple conditionals over nested ternary operators
- Group related code together and separate concerns

### Security
- Add `rel="noopener"` when using `target="_blank"` on links
- Avoid `dangerouslySetInnerHTML` unless absolutely necessary
- Don't use `eval()` or assign directly to `document.cookie`
- Validate and sanitize user input

### Performance
- Avoid spread syntax in accumulators within loops
- Use top-level regex literals instead of creating them in loops
- Prefer specific imports over namespace imports
- Avoid barrel files (index files that re-export everything)
- Use proper image components (e.g., Next.js `<Image>`) over `<img>` tags

### Framework-Specific Guidance
**Next.js:**
- Use Next.js `<Image>` component for images
- Use `next/head` or App Router metadata API for head elements
- Use Server Components for async data fetching instead of async Client Components

**React 19+:**
- Use ref as a prop instead of `React.forwardRef`

**Solid/Svelte/Vue/Qwik:**
- Use `class` and `for` attributes (not `className` or `htmlFor`)
---
## Testing
- Write assertions inside `it()` or `test()` blocks
- Avoid done callbacks in async tests - use async/await instead
- Don't use `.only` or `.skip` in committed code
- Keep test suites reasonably flat - avoid excessive `describe` nesting

## When Biome Can't Help
Biome's linter will catch most issues automatically. Focus your attention on:
1. **Business logic correctness** - Biome can't validate your algorithms
2. **Meaningful naming** - Use descriptive names for functions, variables, and types
3. **Architecture decisions** - Component structure, data flow, and API design
4. **Edge cases** - Handle boundary conditions and error states
5. **User experience** - Accessibility, performance, and usability considerations
6. **Documentation** - Add comments for complex logic, but prefer self-documenting code

---

Most formatting and common issues are automatically fixed by Biome. Run `npx ultracite fix` before committing to ensure compliance.

Best for

These are the workflows where Ultracite adds the most leverage to Jules, based on how the agent reads instructions and how teams typically wire it into day-to-day development.

  1. Queued maintenance work

    • Keep standards stable when Jules handles dependency updates, cleanup tasks, or incremental fixes in the background.

  2. Distributed team handoffs

    • Give every async run the same instructions so results stay consistent even when different teammates trigger the work.

  3. Multi-repo automation

    • Reuse the same AGENTS.md pattern across several codebases where Jules needs clear project-specific expectations.

Why this setup works for Jules

These differentiators come from the way Jules actually handles repo instructions, file updates, and AI-assisted development work.

  • Built for background work

    • Jules runs asynchronously, so shared repo instructions matter more than local IDE settings or one-off chat prompts.

  • Low-friction setup

    • Jules uses AGENTS.md, which keeps the integration simple and portable across repos without another custom config surface.

  • Strong for queued tasks

    • Ultracite helps Jules keep standards intact when it works through queued fixes, migrations, or codebase chores over time.

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