Between 2021 (Copilot) and now, AI assistance moved from a single autocomplete trick to full agents that read your repo, edit files, run tests, and open pull requests. The category is a moving target — products ship monthly, models change quarterly, and the workflow you settle into today will look quaint in a year. The shape, though, is stabilizing.
← Back to Cross-Cutting ToolsThe category-creator (2021). Started as inline tab completion in VS Code; now offers Copilot Chat, multi-file edits, agent mode, and Copilot for the GitHub web UI (PR review, code search). Model choice across Claude, GPT, and Gemini. The default for organizations already standardized on GitHub.
VS Code fork built around AI from the start. Strong reputation for whole-codebase context, multi-file edits, and an agent ("Composer") that plans and applies sweeping changes. Indexes your repo for retrieval and rerank.
Anthropic's terminal-first agent. Runs inside any IDE or in the shell, reads and edits files, runs commands, integrates via the Model Context Protocol (MCP). Designed to be driven from the editor of your choice rather than replace it.
Windsurf (Codeium's editor) emphasizes a "Cascade" agent and was acquired into the Cognition family. Zed bakes AI into a fast native editor. JetBrains AI Assistant + Junie brings agents to the IntelliJ platform. Continue is an open-source extension that lets you bring your own model into VS Code or JetBrains.
| Mode | What it does | Best for |
|---|---|---|
| Tab completion | Inline suggestions a few lines at a time. | Boilerplate, obvious next lines. |
| Chat / inline edit | Ask in natural language; tool proposes a diff you review. | Refactors, "explain this," debugging help. |
| Agent | Tool runs commands, edits multiple files, iterates against tests. | Multi-file features, migrations, repo-wide chores. |
A useful split: tab completion for typing speed, chat for thinking, agents for tasks you'd otherwise spend a half day on.
CLAUDE.md, .cursorrules, Copilot custom instructions — write down conventions, frameworks, and anti-patterns. The agent stops re-deriving them.