Claude Code Architecture Deep Dive

# Pipeline example
tail -f app.log | claude -p "Slack me if you see any anomalies"

# Automation example
claude -p "If there are new text strings, translate them into French and raise a PR"

---
name: code-reviewer
description: Reviews code for quality and best practices
tools: Read, Glob, Grep
model: sonnet
permissionMode: default
skills:
  - api-conventions
hooks:
  PreToolUse:
    - matcher: "Bash"
      hooks:
        - type: command
          command: "./scripts/validate-readonly.sh"
---

You are a code reviewer. When invoked, analyze the code and provide
specific, actionable feedback on quality, security, and best practices.

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          {
            "type": "command",
            "command": "./scripts/validate-edit.sh",
            "timeout": 60
          }
        ]
      }
    ],
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          { "type": "command", "command": "./scripts/run-formatter.sh" }
        ]
      }
    ]
  }
}

{
  "session_id": "string",
  "transcript_path": "/path/to/transcript.jsonl",
  "cwd": "/current/working/directory",
  "permission_mode": "default",
  "hook_event_name": "PreToolUse",
  "tool_name": "Bash",
  "tool_input": {
    "command": "npm run test",
    "timeout": 120000
  },
  "tool_use_id": "toolu_01ABC123..."
}

{
  "continue": true,
  "stopReason": "string",
  "suppressOutput": true,
  "systemMessage": "string",
  "hookSpecificOutput": {
    "hookEventName": "PreToolUse",
    "permissionDecision": "allow|deny|ask",
    "permissionDecisionReason": "string",
    "updatedInput": { "field": "new_value" },
    "additionalContext": "string"
  }
}

#!/usr/bin/env python3
import json
import sys

input_data = json.load(sys.stdin)

if input_data.get("tool_name") == "Write":
    file_path = input_data.get("tool_input", {}).get("file_path", "")
    # Redirect to sandbox
    if file_path.startswith("/etc/"):
        print(json.dumps({
            "hookSpecificOutput": {
                "hookEventName": "PreToolUse",
                "permissionDecision": "deny",
                "permissionDecisionReason": "System directory write blocked"
            }
        }))
        sys.exit(0)

sys.exit(0)

# Add servers
claude mcp add --transport http notion https://mcp.notion.com/mcp
claude mcp add --transport stdio db -- npx @bytebase/dbhub --dsn "postgres://..."

# Manage
claude mcp list
claude mcp get github
claude mcp remove github

# Check status in Claude Code
/mcp

> Can you analyze @github:issue://123 and suggest a fix?
> Compare @postgres:schema://users with @docs:file://api/documentation

> /mcp__github__list_prs
> /mcp__github__pr_review 456

ENABLE_TOOL_SEARCH=auto:5 claude   # Custom 5% threshold
ENABLE_TOOL_SEARCH=true claude     # Always enabled

{
  "mcpServers": {
    "github": {
      "type": "http",
      "url": "https://api.githubcopilot.com/mcp/",
      "headers": {
        "Authorization": "Bearer ${GITHUB_TOKEN}"
      }
    },
    "db": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@bytebase/dbhub", "--dsn", "${DATABASE_URL}"]
    }
  }
}

{
  "permissions": {
    "allow": [
      "Bash(npm run:*)",
      "Bash(git commit:*)",
      "Read(./src/**)"
    ],
    "deny": [
      "Read(./.env*)",
      "Read(./secrets/**)",
      "Bash(rm -rf:*)",
      "Bash(curl:*)"
    ],
    "ask": [
      "Bash(git push:*)"
    ],
    "defaultMode": "default"
  }
}

{
  "permissions": {
    "allow": [
      "Bash(npm run:*)",           // Bash prefix
      "Bash(git * main)",          // Bash glob
      "Read(./src/**)",            // Read directory
      "WebFetch(domain:docs.com)", // WebFetch domain
      "MCP(server:tool)",          // MCP tool
      "Task(Explore)"              // Subagent
    ]
  }
}

#!/usr/bin/env python3
import json
import sys

input_data = json.load(sys.stdin)
tool_name = input_data.get("tool_name")
tool_input = input_data.get("tool_input", {})

# Block sensitive file access
if tool_name == "Read":
    file_path = tool_input.get("file_path", "")
    if ".env" in file_path or "secrets" in file_path:
        print(json.dumps({
            "hookSpecificOutput": {
                "hookEventName": "PreToolUse",
                "permissionDecision": "deny",
                "permissionDecisionReason": "Sensitive file access blocked"
            }
        }))
        sys.exit(0)

sys.exit(0)

---
name: api-developer
description: Implement API endpoints following conventions
agent: general-purpose
---

## Instructions

Follow REST conventions when implementing API endpoints.
Use proper HTTP status codes and error handling.

---
allowed-tools: Bash, Read
---

Run the tests for: $ARGUMENTS

ANTHROPIC_API_KEY=sk-...
CLAUDE_CODE_USE_BEDROCK=true
CLAUDE_CODE_USE_VERTEX=true
CLAUDE_CODE_USE_FOUNDRY=true

ANTHROPIC_MODEL=claude-sonnet-4-5-20250929
ANTHROPIC_DEFAULT_HAIKU_MODEL=claude-3-5-haiku-20241022
ANTHROPIC_DEFAULT_SONNET_MODEL=claude-3-5-sonnet-20241022
ANTHROPIC_DEFAULT_OPUS_MODEL=claude-4-1-opus-20250805
CLAUDE_CODE_SUBAGENT_MODEL=claude-haiku-3-5-20241022

CLAUDE_CODE_MAX_OUTPUT_TOKENS=32000      # Default: 32000, Max: 64000
CLAUDE_CODE_FILE_READ_MAX_OUTPUT_TOKENS=20000
MAX_MCP_OUTPUT_TOKENS=25000
MAX_THINKING_TOKENS=31999
CLAUDE_AUTOCOMPACT_PCT_OVERRIDE=95       # Auto-compaction threshold

BASH_DEFAULT_TIMEOUT_MS=30000
BASH_MAX_TIMEOUT_MS=3600000
BASH_MAX_OUTPUT_LENGTH=100000
CLAUDE_CODE_SHELL=bash

DISABLE_TELEMETRY=1
DISABLE_ERROR_REPORTING=1
DISABLE_AUTOUPDATER=1

{
  "permissions": {
    "allow": [
      "Bash(npm run:*)",
      "Bash(git commit:*)",
      "Bash(docker compose:*)",
      "Read(.)"
    ],
    "deny": [
      "Bash(git push:*)",
      "Bash(rm -rf:*)",
      "Read(.env)",
      "Read(.env.*)",
      "Read(./secrets/**)"
    ],
    "ask": [
      "Bash(git push:*)"
    ],
    "defaultMode": "default"
  },
  "env": {
    "NODE_ENV": "development",
    "CLAUDE_CODE_ENABLE_TELEMETRY": "1"
  },
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          { "type": "command", "command": "./scripts/validate-bash.sh" }
        ]
      }
    ],
    "PostToolUse": [
      {
        "matcher": "Edit|Write",
        "hooks": [
          { "type": "command", "command": "./scripts/format-file.sh" }
        ]
      }
    ]
  },
  "sandbox": {
    "enabled": true,
    "excludedCommands": ["docker"]
  },
  "attribution": {
    "commit": "Generated with Claude Code",
    "pr": ""
  },
  "model": "claude-sonnet-4-5-20250929",
  "language": "english",
  "alwaysThinkingEnabled": false
}