How to Use SKILL.md in Claude, ChatGPT, and Cursor
Most people spend hours tweaking prompts, saving fragments in notes apps, and rewriting the same instructions every time they open a new AI chat. There is a better way: upload a SKILL.md once and let the tool start from the same expert context every time.
A SKILL.md file turns scattered prompt habits into a reusable operating system. Instead of asking the model to “act like a marketer” or “review this code carefully” in every conversation, you encode role, workflow, constraints, examples, and quality standards in one place.
If you have been searching for how to use SKILL.md, custom AI instructions, or the best AI agent setup for Claude, ChatGPT, and Cursor, this guide shows the exact installation patterns that matter.
Claude: Projects Setup, Files, and First Conversation
Claude is one of the cleanest places to use a SKILL.md because Projects let you combine persistent instructions with supporting reference files.
Step-by-step in Claude
Create a Project
Open Claude, choose Projects in the sidebar, and create a project named for the job you want the AI to do, such as Product Marketing, Code Review, or Recruiting Support.
Add project instructions
Open the project settings or instructions area and paste the contents of your SKILL.md into the custom instructions field. This becomes the persistent operating context for every new chat in that project.
Upload supporting files
Add any reference materials that make the skill more useful: style guides, product docs, examples, templates, or SOPs. Keep these separate from the skill file so the reusable operating rules stay clean.
Start a fresh conversation
Begin a new chat inside that project and give Claude a real task. You should not need a long preamble. The point of the SKILL.md is that the setup is already done before the first prompt.
Claude rule of thumb: use the SKILL.md for stable behavior, then use uploaded project files for changing reference context.
ChatGPT: Custom GPTs and Custom Instructions
ChatGPT gives you two useful setup paths. Use a Custom GPT when you want a richer, shareable agent. Use Custom Instructions when you want a fast personal setup.
Option A: Custom GPT
Open My GPTs, create a new GPT, and switch to the configuration view.
Paste your SKILL.md into the Instructions field so the GPT starts with the role, workflow, and constraints baked in.
Add a short name, description, and any tools you want enabled.
Save it and start a new chat with that GPT instead of default ChatGPT.
Option B: Custom Instructions Tab
Open Settings and find the Custom Instructions or Personalization area.
Paste the essential parts of your SKILL.md into the response-style/instructions field.
If the file is too long, keep the role, constraints, workflow steps, and output format, then move examples into your first message or a Custom GPT instead.
Save and start a new conversation so the instructions apply from the beginning.
Custom GPTs are usually the better answer for a full SKILL.md because they give you more room, cleaner reuse, and a dedicated entry point in the ChatGPT sidebar.
Cursor: Add .cursorrules or SKILL.md to the Project Root
Cursor is the most natural fit for instruction files because the rules can live with the codebase and follow the project in version control.
Step-by-step in Cursor
Place the file in the repo root
Add either SKILL.md, .cursorrules, or both at the top level of your project so Cursor can read the rules as project context.
Keep instructions repo-specific
Include coding standards, stack conventions, testing expectations, and file ownership notes that actually apply to that codebase.
Open a new chat or edit session
Start a fresh Cursor chat after adding the file so the assistant picks up the current project rules from the start.
Commit the rules
If the rules are meant for the whole team, commit them. That gives every developer the same AI behavior instead of a private local setup.
Cursor rule of thumb: keep project-specific rules in the repo and generic role guidance in a reusable SKILL.md template that you can adapt across projects.
What Makes a Good SKILL.md
Strong skill files are specific enough to create repeatable behavior but short enough to stay readable and maintainable.
Use a clear structure
Most strong files include role, goals, constraints, workflow steps, output standards, examples, and explicit do-not-do rules.
Keep the core under control
Put evergreen operating instructions in the main file. Move large reference materials into separate documents so the skill file stays focused.
Use placeholders intentionally
If the same skill needs to work across clients or projects, add placeholders for company name, audience, tech stack, or compliance rules so the template can be customized quickly.
Write for action, not theory
Instructions should tell the AI what to do, how to reason about the task, and how to format the result. Generic advice about being helpful is wasted space.
If you want the conceptual background before the setup details, our guide to AI skills and agent configurations explains why this format works so well.
Troubleshooting: Context Limits and When to Split Skills
The file is too long
Trim repeated advice, move long examples to separate files, and keep the main SKILL.md focused on stable operating instructions. Length is only useful when every line changes behavior.
The model ignores part of the instructions
The file is probably too broad or the task is crossing domains. Split a general skill into separate role-specific skills when the workflows or standards differ materially.
Setup works in one tool but not another
That usually means the platform has different instruction limits or a different place for reference files. Keep one core skill, then adapt the installation pattern per platform.
The team keeps editing prompts manually
That is a sign the shared file is missing examples, constraints, or output standards. Improve the source file instead of letting private prompt forks proliferate.
The goal is not to create the longest instruction file possible. The goal is to create a reliable one. When a skill starts serving too many roles at once, split it.
Want a Ready-Made SKILL.md Instead?
SkillPacks give you pre-built expert instruction files for real work, not generic prompting advice. Drop them into Claude, ChatGPT, or Cursor and start from a tested operating system instead of a blank box.
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