Claude Code: What It Is
Anthropic's official agentic CLI for software work.
Claude Code is a terminal-first agent that reads your codebase, runs tools, and edits files. It ships with Read/Write/Edit/Bash/Grep tools and an MCP client so you can add your own.
Real-world example: A Rails 5 → 7 migration
A team uses Claude Code to drive a Rails 5.2 → 7.1 upgrade across a 400K-LOC monolith. They open a worktree, point Claude Code at it, and run:
> Read config/application.rb. Find every deprecated API usage that needs updating for Rails 7.1. Group them by file and produce a migration checklist.Claude reads, greps, writes a checklist. Then for each entry it edits, runs the spec file for that area, and reports back. The senior engineer reviews diffs in the IDE. The whole upgrade lands in a week instead of two months.
Why this matters: Claude Code is most valuable on bounded, well-tested refactors. The harness lets the model do the boring 80% while you spend your attention on the genuinely tricky 20%.
- Claude Code is Anthropic's agentic CLI
- Ships with Read/Write/Edit/Bash/Grep tools
- Acts as an MCP client for added tools
- Reads codebase, runs tools, edits files
- Terminal-first, not GUI-first