CLAUDE.md vs .cursorrules: Which Brand Format Do You Need?

Two formats, one goal

Both CLAUDE.md and .cursorrules tell AI agents how your brand sounds, looks, and decides. But they are designed for different tools, different contexts, and different audiences within your organization. Understanding where each file shines — and where they overlap — is the difference between partial governance and complete control.

88% of companies now use AI tools daily. Most of those teams use more than one tool. A marketing team on ChatGPT, an engineering team on Cursor, a product team on Claude. Each tool has its own instruction mechanism. Without a deliberate strategy, brand rules fragment across tools, and nobody notices until the output is already published.

CLAUDE.md — Universal agent instructions

CLAUDE.md is the general-purpose brand rulebook. It works with any LLM-backed agent: Claude Code reads it automatically from your repo root, but the same file can be pasted into ChatGPT Custom Instructions, Copilot settings, or any tool that accepts a system prompt.

Use CLAUDE.md when:

• You want brand rules that work across multiple AI tools
• You are building for remote teams or agencies managing many clients
• Brand governance is a cross-organizational concern
• You need a single, canonical source of truth for how your brand sounds

What goes in a CLAUDE.md:

• Voice and tone definitions (default, support, marketing, technical)
• Visual constraints (color roles, typography, spacing)
• Messaging hierarchy (taglines, value propositions, proof points)
• Brand rules and explicit do/don't patterns
• Context-specific guidance for different communication channels

# Brand Guidelines

## Voice
Default: clear, confident, evidence-led.
Support: empathetic, concise, action-oriented.
Marketing: bold claims require data. No superlatives.
Technical: precise, factual, never casual.

## Visual
Primary #9C4221 — CTAs and interactive elements only.
Accent #D97706 — highlights, success states, secondary emphasis.
Typography: Instrument Serif (headlines), DM Sans (body), JetBrains Mono (code).
Border radius: 4px consistently. Not bubbly, not sharp.

## Rules
- Never use exclamation marks in headlines.
- Data claims must include a source or qualifier.
- Support responses always end with a next step.

For a complete walkthrough of every section, see our CLAUDE.md writing guide.

.cursorrules — Editor-specific governance

.cursorrules is Cursor's native instruction file. It lives in your project root and governs everything Cursor does: code completion, chat responses, and agentic refactoring. It is editor-first and code-first.

Use .cursorrules when:

• Your team primarily uses Cursor as their code editor
• You want project-specific, code-level conventions enforced automatically
• Component naming, file structure, and import patterns matter
• You need CSS and design token conventions alongside brand voice

What goes in a .cursorrules file:

• Coding standards and architectural patterns
• Component naming conventions (PascalCase, kebab-case, etc.)
• File structure and organization rules
• Design token references and CSS conventions
• Brand voice as it applies to code output (comments, variable names, error messages, UI strings)

# Cursor Rules

## Component naming
- React components: PascalCase (e.g., BrandCard, PricingTier)
- CSS classes: kebab-case via Tailwind utilities
- Files: match the default export (PascalCase for components)
- Hooks: use prefix (e.g., useBrandTheme, useScrollProgress)

## Design tokens
- Always reference CSS variables, never hardcode hex values
- Primary: var(--color-primary) not #9C4221
- Spacing: use Tailwind scale (py-6, gap-4), never arbitrary px

## Typography
- Headlines: font-display (Instrument Serif), tracking-tight
- Body: font-body (DM Sans), text-base or text-lg, leading-relaxed
- Code: font-mono (JetBrains Mono), text-sm

## Voice in generated code
- Error messages: concise, helpful, never use ALL CAPS
- Comments: clear and technical, no humor or colloquialisms
- UI labels: sentence case, action-oriented ("Save changes" not "Submit")

The practical difference

Imagine you are a developer working in a branded codebase. The impact of these files becomes obvious when you compare scenarios:

Without either file:

• Cursor suggests code with hardcoded colors and arbitrary fonts
• Claude generates marketing copy that drifts from your voice
• You manually adjust everything after generation
• New team members have no idea what the conventions are

With CLAUDE.md only:

• Claude respects your brand voice across all content generation
• But Cursor still suggests off-brand code — wrong tokens, wrong naming
• You have to remember component naming rules yourself

With .cursorrules only:

• Cursor respects code conventions and design token references
• But Claude does not know your brand voice
• Remote teams and ChatGPT users are left out entirely

With both files in your repo:

• Cursor enforces project conventions in every code suggestion
• Claude enforces brand voice in every content generation
• Copy, code, and components all align automatically
• New team members clone the repo and understand everything immediately

The difference is not marginal. Teams using both files report 60% fewer brand-related corrections in code review and content review cycles.

How they complement each other

Think of CLAUDE.md as the signal and .cursorrules as the filter.

CLAUDE.md says: "We sound clear, confident, and evidence-led." .cursorrules says: "In this codebase, that means: descriptive variable names, clear JSDoc comments, and error messages that suggest a next step."

CLAUDE.md says: "Primary color is #9C4221, reserved for CTAs." .cursorrules says: "Reference it as var(--color-primary) in CSS, never hardcode hex values. Use the bg-primary Tailwind class."

CLAUDE.md says: "Headlines use Instrument Serif." .cursorrules says: "Apply font-display class to all h1 and h2 elements. Never import Google Fonts — use Fontsource."

The brand instruction travels from the high-level (CLAUDE.md) to the implementation-specific (.cursorrules). They reference each other. They reinforce each other. And because both are plain text files in the repo, any change is a diff that can be reviewed, approved, and traced.

Where AGENTS.md fits in

If you are also using AGENTS.md, the hierarchy becomes:

1. AGENTS.md — operational governance: what agents can and cannot do, approval gates, audit trail
2. CLAUDE.md — brand governance: how output should sound, look, and behave
3. .cursorrules — implementation governance: code-level conventions, token references, file structure

Each layer is owned by a different team. Platform engineers own AGENTS.md. Brand managers own CLAUDE.md. Technical leads own .cursorrules. All three live in version control, all three are machine-readable, and all three update when the brand evolves.

BrandMythos generates both automatically

When you upload a brand guide to BrandMythos, we extract your voice rules, visual constraints, and messaging hierarchy. From that single extraction, we generate:

1. CLAUDE.md — the universal version that works with any AI tool
2. .cursorrules — the project-specific version tailored for Cursor's code completion
3. AGENTS.md — operational governance with your brand rules embedded
4. Design tokens — CSS variables and Tailwind config for implementation
5. System prompts — for ChatGPT, Gemini, and Copilot custom instructions

All files sync to your repos. All are versioned. All update automatically when you change brand rules in the dashboard. See every output format we support.

Recommendation

Start with CLAUDE.md. It is the foundation and works with every AI tool your team uses. If you only adopt one file, make it this one.

Add .cursorrules when your engineering team uses Cursor as the primary editor, or when code-level conventions need enforcement alongside brand rules.

Use both for complete governance: brand at the strategic layer, code conventions at the implementation layer, everything versioned and in sync.

Try BrandMythos with your brand. We generate both files from your existing brand guide in minutes — no manual authoring required.