# How Claude Code Works Internally: CLI Startup, Tools, SDK, and Agent Runtime

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## Article Metadata
- Title: How Claude Code Works Internally: CLI Startup, Tools, SDK, and Agent Runtime
- Summary: A practical systems-level explanation of Claude Code as a local agent runtime, covering startup, authentication, tools, permissions, sessions, MCP, plugins, and the Agent SDK.
- Published: May 20, 2026, 3:31 PM EDT
- Updated: May 20, 2026, 3:31 PM EDT
- Category: AI Security
- Primary topic: Claude Code
- Authors: Owen Park
- Read time: 13 min
- Language: en_US
- Publication time zone: America/New_York (U.S. Eastern Time)
- Access: Free to read

## Topic Links
- [AI Security](https://threatfrontier.com/categories/ai-security): Category archive for related coverage.
- [Claude Code](https://threatfrontier.com/tags/claude-code): 1 public article in this topic.

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