How Claude Code works in large codebases: Best practices and where to start

Anthropic shares best practices for deploying Claude Code in large-scale engineering environments including multi-million-line monorepos, legacy systems, and distributed microservice architectures. The core insight is that the 'harness' around the model matters more than the model itself. Key components include: CLAUDE.md context files (layered from root to subdirectory), hooks for self-improvement and automation, skills for on-demand expertise loading, plugins for distributing working setups org-wide, LSP integrations for symbol-level navigation, MCP servers for internal tool access, and subagents for splitting exploration from editing. Practical guidance covers keeping CLAUDE.md files lean, scoping commands per subdirectory, using .ignore files, building codebase maps, and running LSP servers. Organizational patterns are also addressed: successful rollouts invest in infrastructure before broad access, assign dedicated ownership (sometimes an 'agent manager' role), and establish cross-functional working groups for governance.