GitHub Copilot

GitHub Copilot is the most widely deployed AI coding assistant: inline tab completions plus chat in editors you already use.

Copilot Modes

Inline completions are low-risk because you accept line by line. Agent-style edits need the same verification checklist as any AI tool.

Effective Inline Use

Copilot learns from open files and nearby code. Help it help you:

1. Write a comment or function signature first to describe intent before implementation
2. Keep related files open so context improves suggestions
3. Use descriptive names: fetchUserOrdersWithRetry beats getData
4. Tab only what you understand and reject suggestions that import unknown packages

// Fetch paginated orders for a user; handle 404 as empty array
async function fetchUserOrders(userId, page = 1) {
  // Copilot completes from here. Review error handling.
}

Custom Instructions (.github/copilot-instructions.md)

Teach Copilot your stack and conventions with a repo-level instructions file. This is equivalent to Cursor's .cursor/rules/ — Copilot reads it automatically:

<!-- .github/copilot-instructions.md -->

# Project Conventions

## Stack
- Next.js 15 App Router, React 19, TypeScript strict
- Drizzle ORM with Postgres
- Tailwind CSS v4
- Zod for all input validation

## Code Style
- Named exports only (no default exports except page.tsx / layout.tsx)
- Server components by default; add "use client" only when state or browser APIs are needed
- Colocate tests: src/lib/foo.test.ts alongside src/lib/foo.ts

## Patterns to Follow
- Auth check on every API route: `const session = await auth()`
- Validate all external input with Zod before using it
- Use `Response.json()` for API route responses, not `NextResponse`

## Things to Avoid
- Do not add new npm packages without asking
- Do not modify drizzle/migrations/** or package-lock.json
- Do not use `any` in TypeScript

Copilot uses this file for both inline completions and chat suggestions. Keep it under ~500 tokens — long files get truncated. Docs: GitHub custom instructions.

Copilot Chat Prompts

Structure chat like a code review request:

In src/utils/date.ts, add a function formatRelativeTime(iso: string): string
using Intl.RelativeTimeFormat. Match existing error handling. Do not add dependencies.

Avoid: "make this better" or "fix everything."

For debugging, paste the full error:

This function throws "Cannot read properties of undefined (reading 'map')"
when orders is null. Fix with a null guard. Do not change the return type.

@src/components/OrderList.tsx

Learning New APIs

Copilot is useful for unfamiliar syntax, but it hallucinates APIs as often as other models. Always verify against official docs. The combination of Copilot suggestion + official docs check is faster than either alone.

Pricing Overview (2026)

Typical tiers (confirm on GitHub):

• Free: limited completions and chat
• Pro: unlimited completions, more premium requests
• Business / Enterprise: policy controls, IP indemnity options

Students, teachers, and maintainers of popular open-source projects often qualify for free access.

Copilot vs IDE Agents

Copilot optimizes for speed inside your editor. Cursor and Claude Code optimize for autonomous multi-step tasks. Many developers use Copilot for completions plus a separate agent for larger features.

See Choosing a Tool.

Related

• OpenAI Codex
• Cursor
• Prompting for Code
• Project Rules
• Common Mistakes in AI-Generated Code
• Choosing a Tool