docs/content/copilot/tutorials/customization-library/custom-instructions/your-first-custom-instructions.md

title, intro, versions, category, complexity, octicon, topics

title	intro	versions	category	complexity	octicon	topics
Your first custom instructions	Create and test your first custom instruction with this simple example.	feature copilot	Custom instructions Getting started Configure Copilot	Simple	book	Copilot

{% data reusables.copilot.customization-examples-note %}

About customizations

You can customize {% data variables.product.prodname_copilot %}'s responses using two types of files:

• Custom instructions provide ongoing guidance for how {% data variables.product.prodname_copilot %} should behave across all your interactions.
• Prompt files (public preview) define reusable prompts for specific tasks that you can invoke when needed. {% data reusables.copilot.prompt-files-available-in-editors %} For an introductory example, see AUTOTITLE.

While custom instructions help to add context to each AI workflow, prompt files let you add instructions to a specific chat interaction.

Repository custom instructions are the most commonly used and supported, but you can also define personal and organization custom instructions, only for {% data variables.copilot.copilot_chat_dotcom %}. {% data reusables.copilot.repository-custom-instructions-types %}

Your first instructions

Start with these core custom instructions that helps {% data variables.product.prodname_copilot %} understand your coding preferences.

Instructions on writing functions

When writing functions, always:
- Add descriptive JSDoc comments
- Include input validation
- Use early returns for error conditions
- Add meaningful variable names
- Include at least one example usage in comments

These instructions will change how {% data variables.product.prodname_copilot %} generates functions.

Test it out

To quickly test out the difference that custom instructions can make, you can use personal custom instructions in {% data variables.copilot.copilot_chat_short %}'s immersive view.

1. First, go to github.com/copilot and enter this prompt:

   Create a JavaScript function that calculates the area of a circle

   Without custom instructions, you might get:

   function areaOfCircle(radius) {
       if (typeof radius !== 'number' || radius < 0) {
           throw new Error('Radius must be a non-negative number');
       }
       return Math.PI * radius * radius;
   }
   

2. Now access your personal custom instructions by clicking on your profile picture in the bottom left of the page, then click Personal instructions. Paste the above instructions into the text box, then click Save.

   Now enter the same prompt that you entered previously.

   With custom instructions, you'll get something like:

   /**
    * Calculates the area of a circle given its radius.
    *
    * @param {number} radius - The radius of the circle. Must be a positive number.
    * @returns {number|null} The area of the circle, or null if the input is invalid.
    *
    * @example
    * // returns 78.53981633974483
    * areaOfCircle(5);
    *
    * @example
    * // returns null (invalid input)
    * areaOfCircle(-2);
    */
   function areaOfCircle(radius) {
     if (typeof radius !== "number" || isNaN(radius) || radius <= 0) {
       // Invalid input: radius must be a positive number
       return null;
     }
   
     const area = Math.PI * Math.pow(radius, 2);
     return area;
   }
   
   // Example usage:
   console.log(areaOfCircle(5));   // 78.53981633974483
   console.log(areaOfCircle(-2));  // null
   

{% data reusables.copilot.custom-instructions-further-reading %}