MCP Integration Skill

Principle: #34 (Occam's Razor Implementation)

Source: Empirical testing in claude-code-playground (2026-01-27/28). 12 tests across agent-kernel and blackboard MCPs.

When to Use This Skill

Use the mcp-integration skill when:

• Adding a new MCP server to a project
• Claude doesn't use MCP tools as expected
• Debugging why an MCP works in one project but not another
• Optimizing MCP config (removing unnecessary layers)

DO NOT use this skill for:

• Building MCP servers (use MCP SDK docs)
• General Claude Code configuration (not MCP-specific)

The Escalation Ladder

Level 0: .mcp.json only           <- Start here (always)
Level 1: + CLAUDE.md paragraph    <- Most tools land here
Level 2: + UserPromptSubmit hook  <- For protocol enforcement
Level 3: + Hook script            <- For context pre-loading
Level 4: + allowedTools           <- For permission issues
--------------------------------------------------
Level 5: Approach limitation      <- Stop. Rethink.

Level 0: MCP Registration Only

Add: .mcp.json

{
  "mcpServers": {
    "my-mcp": {
      "command": "node",
      "args": ["path/to/build/index.js"]
    }
  }
}

Test: Ask Claude to explicitly use a tool from this MCP.

Works when: User explicitly requests tool functionality.

Evidence: Test 2.1 — Blackboard contribute_fact worked with zero config when prompt explicitly asked to "contribute a fact".

Escalate when: Claude doesn't use MCP tools spontaneously (without explicit mention).

Level 1: + CLAUDE.md Instruction

Add: A short paragraph in CLAUDE.md expressing intent (not API reference).

## [MCP Name]

BEFORE starting work, [do X with MCP tool].
AFTER completing work, [do Y with MCP tool].

Test: Give Claude a task where the MCP is relevant but not mentioned in the prompt.

Works when: Claude spontaneously uses MCP tools at appropriate moments. Works in both interactive and pipe (-p) mode.

Evidence: Test 9 — Claude spontaneously called list_sessions + read_facts when CLAUDE.md said "check blackboard before work", even though the prompt only said "review sample_code.py".

Key insight: Express intent ("check for prior context"), not API ("call mcp__blackboard__list_sessions"). Claude discovers tool names from MCP registration.

Escalate when: Claude reads instruction but doesn't reliably follow it (inconsistent adoption).

Level 2: + UserPromptSubmit Hook (Inline)

Add: .claude/settings.json with inline hook.

{
  "hooks": {
    "UserPromptSubmit": [{
      "hooks": [{
        "type": "command",
        "command": "cat <<'EOF'\n{\"additionalContext\":\"<system-instruction>\\nYou MUST call tool_x before work.\\n</system-instruction>\"}\nEOF"
      }]
    }]
  }
}

Test: Run several tasks and verify tool is called every turn.

Works when: Need mandatory protocol enforcement (e.g., agent-kernel tuple_init/evaluate_gradient on every turn).

Evidence: Tests 2-3 — Agent-kernel protocol was reliably enforced with hook injection. Without hooks (tests 1-5), CLAUDE.md alone was insufficient for per-turn protocol compliance.

Limitation: Hooks do not fire in pipe mode (claude -p "..."). Only interactive sessions.

Escalate when: Need to pre-load context (not just instructions), or need optimization.

Level 3: + Hook Script (Context Injection)

Add: Replace inline hook with a script.

{
  "hooks": {
    "UserPromptSubmit": [{
      "hooks": [{
        "type": "command",
        "command": "bash scripts/context-hook.sh"
      }]
    }]
  }
}

The script reads state files and outputs JSON with additionalContext containing pre-loaded data.

Works when: Reduces tool calls by injecting data that would otherwise require tool calls (e.g., blackboard facts as <episodic-memory> tags).

Evidence: blackboard-context-hook.sh saves 2 tool calls per turn by pre-loading facts.

Limitation: Still doesn't fire in pipe mode. Adds shell execution latency.

Escalate when: Permission denials prevent tool usage.

Level 4: + Explicit allowedTools

Add: Permission grants in .claude/settings.json.

{
  "permissions": {
    "allow": ["mcp__my-mcp__*"]
  }
}

Works when: Removes permission prompts that cause Claude to abandon tool usage.

Evidence: Test 2 showed Claude attempted agent-kernel tools but was DENIED by permissions.

This is the last configuration lever.

Level 5: Approach Limitation

If all levels active and Claude still doesn't use the MCP as intended:

Quick Decision Matrix

Patterns (from empirical testing)

P1: CLAUDE.md is the Universal Injection Mechanism

Loads in every mode (interactive, pipe, Task agents). Hooks only fire in interactive mode. For guaranteed behavior across all contexts, CLAUDE.md is the foundation.

P2: Hooks Complement, Don't Replace

Hooks add enforcement (Level 2) and optimization (Level 3) on top of CLAUDE.md. Not a substitute — pipe mode proves this.

P3: Tool Discovery is Automatic

Claude discovers MCP tools from registration alone. Never list tool names in CLAUDE.md. Express intent, not API reference.

P4: Spontaneous != Explicit

Write path (explicit request -> tool use) works at Level 0. Read path (spontaneous retrieval) requires Level 1 minimum.

P5: Escalation is Reversible

If Level 1 sufficient after testing Level 2, remove the hook. Keep config minimal.

Test Protocol (for new MCP servers)

1. Register in .mcp.json only (Level 0)
2. Test: Does Claude use tools when explicitly asked?
   -> YES: Level 0 sufficient for explicit use
   -> NO: Fix MCP tool schema/description

3. Add CLAUDE.md paragraph (Level 1)
4. Test: Does Claude use tools spontaneously?
   -> YES: Done. Level 1 is your config.
   -> NO: Escalate

5. Add UserPromptSubmit hook (Level 2)
6. Test: Is protocol enforced per turn?
   -> YES: Done.
   -> NO: Check hook JSON format

7. Add hook script (Level 3) — only for context pre-loading
8. Add allowedTools (Level 4) — only for permission denials

9. All levels exhausted? -> Level 5: Rethink approach

Anti-Patterns

A1: Cargo-Cult Configuration

Adding all levels at once "just in case".

A2: Tool API Docs in CLAUDE.md

Listing every tool name and parameter. Claude gets this from MCP registration. CLAUDE.md should express intent.

A3: Hook Without CLAUDE.md

Relying only on hooks. Breaks in pipe mode and Task agents.

A4: Assuming Failure Without Testing

Jumping to Level 3 without observing Level 0 behavior first.

Evidence Source

All findings from systematic testing in claude-code-playground:

• Tests 1-9: Agent-kernel MCP adoption
• Tests 2.1-2.3: Blackboard MCP adoption
• Tests 4-9: Blackboard read path (spontaneous retrieval)
• See claude-code-playground/docs/TEST_FINDINGS.md for raw data