The rules that apply within your project are described in files with the extension .mdc inside the .cursor/rules folder. Let's create a new rule file to set the coding standards for the project.

Create a new file in the .cursor/rules folder and name it coding-standards.mdc. Or ask Cursor to create it for you.

Create a file coding-standards.mdc in .cursor/rules folder with these instructions: #Python Coding Standards: - Use 4 spaces for indentation - Maximum line length of 88 characters - Follow PEP 8 naming conventions - Use descriptive variable and function names - Add docstrings for all functions and classes - Imports in order: standard library, third-party, local application - Use type hints for function parameters and return values These standards ensure readability and consistency throughout our codebase.

Now let's define the rule type for this file.

Always - rules are applied always and to any files in the project
Auto Attached - rules are applied only to files that fit the pattern specified in the settings
Agent Requested - whether to read or not to read the rule, whether to apply it within a particular request or not will be decided by the agent based on the description you specify in the rule. For example, if the description contains standards for the Python language, the agent will pay attention to these rules when creating files in this language
Manual - the agent will apply the rule only if you mention the rule in the request using the @ symbols

⚠️ “Always” applied rules consume extra tokens on every call — we recommend to keep them short (<≈ 500 lines) or Cursor may truncate them.

The Cursor interface hides the textual definition of these rules, but if you open an .mdc file in another editor, you will see options at the beginning of the file that specify these settings:

alwaysApply (Boolean) - set to true to make the rule type Always (injected into every AI request). Leave as false when the rule should load conditionally (Auto-Attached, Agent-Requested, or Manual).
globs (String[]) - an array of file-path patterns that trigger an Auto-Attached rule. Supports wildcards (*, **) and negation (!tests/**).
description (String) - a one-line summary the agent matches on. Mandatory for Agent-Requested rules and recommended for all rules to improve relevance.

If alwaysApply: true the rule type is Always (loaded on every request). If alwaysApply: false and you supply a globs array, it’s Auto-Attached (loads only when the active file matches). If alwaysApply: false with no globs, Cursor treats it as Agent-Requested—the agent decides to load it when the description seems relevant (so keep that line concise and descriptive). Any other combination defaults to Manual; you must reference it in chat with @RuleName to load it.

The hidden markup of the rules files make it hard for agents to change them via agent command. To reliably set the rule type we recommend to do it via Cursor UI.

Now let's set the Rule Type for the @coding-standards.mdc file to Auto Attached with pattern **/*.py:

Using these setting allows the rule to be applied only to Python files.

If you need other files, you can list them too. Here are examples:

*.py - matches all Python files
* - matches all files
src/*.py - matches Python files in the src folder
**/*.py - matches Python files in any folder
test_*.py - matches Python files that start with "test_"

Completion Checklist

Next, we'll create some code to test our rule.

Introduction to Cursor Rules