You can lose a reader's trust in one sentence. Jules, a developer on a three-person team, almost did. The repo uses TypeScript, and tests live next to the file they cover. Nobody asked the assistant to redesign the app. The draft said "I added a new state library and opened a pull request." The source never did.
After this guide you will be able to explain Cursor rules in your own words, copy a prompt that fits the job, and catch the extra sentence before anyone else sees it.
What Is Cursor Rules?
Cursor rules means using an AI tool to write a short rules file from the repo's real habits, while a person checks every factual line against a source.
It is not a magic phrase you drop into a chat. It is a short method: one job, one source, one shape, one ban, and one human send. Jules, a developer on a three-person team, is a clear picture of the method. You already have this in the source: TypeScript, tests beside the file, and no new dependency without asking. The draft is only useful if it stays inside that.
This matters now because the tools are easy to open and the extra sentence is easy to miss. A beginner can produce a page that sounds finished. Sound is not the same as truth. If you remember one definition, remember this: a good draft is one you can point at.
Why Cursor Rules Matters
- You start from something true. You already have this in the source: TypeScript, tests beside the file, and no new dependency without asking. The guide keeps the draft tied to that, instead of asking the tool to invent a better story.
- You can see the mistake. The mistake in this story is easy to quote: "I added a new state library and opened a pull request." Once you can quote it, you can delete it. Vague worry is harder to edit.
- You get a prompt you can reuse. The prompt below is written for this job. Next time you change the notes, not the rules.
- A person still owns the send. Do not let a coding agent commit, push, or add dependencies without a person. The tool can draft. It cannot be the name on the email, the post, the file, or the decision.
People searching for cursorrules examples or AI coding rules for a repo are usually stuck on the same gap. They have notes. They do not have a safe way to turn the notes into something they can send. The method below is that way.
How Cursor Rules Works
- Name one job before you name a tool. The job here is simple: write a short rules file from the repo's real habits. Cursor rules starts after that sentence exists. Why it matters: A tool list feels like progress, but the blank page is still there.
- Show the source, then ask for a shape. The repo uses TypeScript, and tests live next to the file they cover. Nobody asked the assistant to redesign the app. The shape is short enough that a colleague can check it quickly. Why it matters: The tool cannot be careful about a fact you never gave it.
- Hunt for one extra sentence. Delete "I added a new state library and opened a pull request." and read what remains. If the piece still does the job, that line was never needed. Why it matters: Most bad drafts are fine except for one confident addition.
Treat Cursor as a fast typist and yourself as the editor. Typists are quick. Editors decide what is true. Cursor rules goes wrong when the typist is also allowed to invent the facts.
Start with the source on the screen, not in your memory. The repo uses TypeScript, and tests live next to the file they cover. Nobody asked the assistant to redesign the app. Memory drops a date and adds a guess. The screen does not.
Then ask for a marked draft. Say: if a line is not supported, write "not in the source" instead of filling it. The line you are practicing on is "I added a new state library and opened a pull request." Do not let a coding agent commit, push, or add dependencies without a person.
Rules are a fence around habits you already have, not a wish for a new architecture. Jules knows where tests live. Write that down so the assistant stops inventing a second style. The dangerous sentence is the one where the tool 'helps' by adding a library and opening a pull request. Helping, here, means asking. Commit stays a human verb.
The editor's last pass is short. Read it aloud. Listen for a promise, a number, a person, or a cause you did not supply. GitHub Copilot is useful here because a second tool will often mark the line you got used to. You still make the cut. A second tool is not a second witness.
A Prompt You Can Copy
Use this with Cursor. Replace the notes. Do not delete the ban.
Write a short rules file. We use TypeScript. Tests live next to the file. Do not add dependencies, change public APIs, or commit without asking. Do not invent extra habits.The weak prompt, for contrast, was: "Scan the repo and modernize everything." Keep the weak one in your head only as a warning. Do not paste it.
Best Tools for Cursor Rules
You do not need a large stack. Three tools cover the job. If you are choosing software for a whole company, start with the company buying shortlist after you can do this one task by hand.
Cursor
Cursor reads a rules file from the project if you keep it short.
Best for: a first draft when you already have the source
Price: Cursor lists a lower Plus plan and a higher Premium plan. Extra models can cost more. Confirm on Cursor's pricing page.
How it helps: It turns the source into a draft of this job: write a short rules file from the repo's real habits.
Good to know: Do not let a coding agent commit, push, or add dependencies without a person.
GitHub Copilot
GitHub Copilot should follow the same habits when you ask for a completion.
Best for: a colder edit after the first draft
Price: GitHub Copilot Pro was about $10 a month on GitHub's plan page. Confirm before you buy.
How it helps: It is good at listing lines that add a fact, including a line like "I added a new state library and opened a pull request."
Good to know: Do not let a coding agent commit, push, or add dependencies without a person.
Claude Code
Claude Code can draft the rules text, which a person then commits.
Best for: a last pass in the tool that fits this file
Price: Check the current price on the vendor page before you buy. This guide does not invent a seat price.
How it helps: It can draft the rules text, which a person then commits.
Good to know: Do not let a coding agent commit, push, or add dependencies without a person.
Step-by-Step: How to Get Started
Step 1: Write the job in one line
Write: write a short rules file from the repo's real habits. Put that line above the chat. If you need a second sentence to explain the goal, you are mixing two tasks. Split them. Cursor rules works on one task at a time.
Step 2: Bound the source
The repo uses TypeScript, and tests live next to the file they cover. Nobody asked the assistant to redesign the app. Copy only what you are allowed to share. Keep TypeScript, tests beside the file, and no new dependency without asking visible. Remove passwords, customer lists, health details, and legal files you do not have permission to upload.
Step 3: Use a prompt that draws a fence
Do not start with "Scan the repo and modernize everything." That prompt asks for a nice tone and leaves the facts open. Paste the prompt from the section above. Then replace the notes with yours.
Step 4: Keep only the version you can point at
Do not let a coding agent commit, push, or add dependencies without a person. Read every factual line and point at the source. The version you keep must pass this test: The rules name TypeScript, colocated tests, and a ban on surprise dependencies. You send it. The model does not.
When the same shape comes up every week, copy a workflow or a prompt template instead of starting from a blank chat. Change the source. Keep the ban.
Real Examples
Example 1: Jules
Situation: The repo uses TypeScript, and tests live next to the file they cover. Nobody asked the assistant to redesign the app.
What to do: Use the prompt above. Tell the tool the job is to write a short rules file from the repo's real habits. Reject any line like "I added a new state library and opened a pull request."
Why this works: Do not let a coding agent commit, push, or add dependencies without a person
Result: The rules name TypeScript, colocated tests, and a ban on surprise dependencies.
Example 2: A student
Situation: The class repo must not add packages the grader did not list.
What to do: The rules say ask before any package.
Why this works: A surprise package can fail the grader.
Result: The project stays on the allowed list.
Example 3: A freelancer
Situation: The client's repo has a lint script they must not bypass.
What to do: The rules say run lint, do not disable it.
Why this works: A skipped lint hides the bug the client pays to prevent.
Result: Lint stays on.
These are practice examples, not customer results. The test is the same in each one: if you cannot point at the source, it does not ship.
Common Mistakes to Avoid
- Opening with "Scan the repo and modernize everything.". The tool fills the silence with a confident extra claim. Do this instead: Name the job, the source, the length, and the ban in the same prompt.
- Leaving "I added a new state library and opened a pull request." because it sounds polite. Polite and untrue is still untrue. The reader may act on it. Do this instead: Delete it, even if the paragraph feels shorter.
- Pasting a whole inbox, folder, or database. You only need TypeScript, tests beside the file, and no new dependency without asking. Extra text gives the tool more chances to grab the wrong fact. Do this instead: Paste the smallest source that still contains the detail.
- Asking the tool to pick a plan, a price, or a legal conclusion. Those are decisions. A draft can list what the source says. It cannot make the decision for you. Do this instead: Write 'not in the source' and decide yourself, or ask the person who owns the decision.
Quick Comparison
| Option | Best for | Difficulty | Cost | Beginner tip |
|---|---|---|---|---|
| Cursor | First draft from a small source | Easy | Free plan, paid if you need more | Paste less than you think |
| GitHub Copilot | Second pass on a smooth draft | Easy | Check the vendor page | Ask it to mark new claims |
| Claude Code | can draft the rules text, which a person then commits. | Easy | Check the vendor page | Do not move secrets into a personal login |
Tips That Actually Help
- Tip 1. Keep TypeScript, tests beside the file, and no new dependency without asking in the first three lines of the prompt so the model cannot skip it.
- Tip 2. Ten lines of rules beat a manifesto. If a rule is not true this week, delete it.
- Tip 3. If the draft uses a number, a date, or a name, find it in the source before you keep it. "I added a new state library and opened a pull request." fails that test.
- Tip 4. Run the same notes through GitHub Copilot only after the first draft exists. A second tool is an editor, not a new source of facts.
- Tip 5. Save the prompt in your notes or in the prompt library. Next week, swap the source and keep the ban: Do not let a coding agent commit, push, or add dependencies without a person.
FAQ
What is the practical way to do Cursor rules?
Start with one source. The repo uses TypeScript, and tests live next to the file they cover. Nobody asked the assistant to redesign the app. Ask for a draft of this job: write a short rules file from the repo's real habits. Then delete any line the source does not support. The line to practice on is "I added a new state library and opened a pull request." The version you keep should match this: The rules name TypeScript, colocated tests, and a ban on surprise dependencies.
Why did the draft say "I added a new state library and opened a pull request."?
Because the first prompt was too open. "Scan the repo and modernize everything." asks for a polished result and does not forbid new claims. The tool prefers a complete sound. Do not let a coding agent commit, push, or add dependencies without a person. Put that ban in the prompt, then check the draft yourself.
Which tool should I open first?
Open Cursor for the first shape. Open GitHub Copilot when the draft sounds sure and you want extra lines marked. Open Claude Code when the work should stay in that product or needs a different kind of pass. Confirm the live price before you buy.
What should never go into the prompt?
Do not let a coding agent commit, push, or add dependencies without a person. Also leave out passwords, payment data, private customer lists, and health or legal records you are not allowed to upload. If you would not email it to a stranger, do not paste it.
Is this useful for a complete beginner?
Yes. You only need an account and one real note. Jules, a developer on a three-person team is not an expert in the story. The skill is the check, not a secret setting. You can practice on a free plan, then pay only if a limit blocks a real task.
The Bottom Line
Cursor Rules is a small, strict way to write a short rules file from the repo's real habits. Jules, a developer on a three-person team, almost sent "I added a new state library and opened a pull request." because the first prompt was vague. The fix was not a new subscription. The fix was a source, a ban, and a read-aloud.
Your next step is small. Open Cursor, paste the prompt, and use a note you already have. Keep the draft only if this is true: The rules name TypeScript, colocated tests, and a ban on surprise dependencies.
For more walkthroughs, browse the AI tools directory and these related guides: How to Start Using AI Tools and Pull Request Text a Reviewer Can Test.