MCP

Model Context Protocol servers extend Claude Code with tools, resources, and prompts. This skill covers selection, configuration, and the three server primitives.

The three primitives

Primitive	Loaded when	Use for
Tools	Always (metadata in context)	Actions Claude can take (read/write/query)
Resources	On request	Static content Claude can list and fetch
Prompts	On request	Pre-composed conversation starters for complex workflows

Cost model: historically every tool's name + description + JSON schema consumed context every turn. As of 2026, Claude Code defers tool schemas by default and discovers them via ToolSearch (see below), so the per-turn drain is mostly limited to built-ins and alwaysLoad servers. Still prefer MCP Prompts/Resources for heavy reference material Claude loads only when asked.

Configuration files

File	Scope	When
~/.claude/mcp.json (or equivalent)	Global	Servers you want in every project
.mcp.json (in repo root)	Project	Servers specific to this repo
.mcp.local.json	Personal override	User-local, gitignored

Project-scoped is almost always better — avoids global context cost when you're not in that project.

Transports

Transport	When
stdio	Local servers; fastest; the default for plugin/child-process servers
http	Remote servers — recommended for cloud-hosted MCPs; supports OAuth and async reconnection
sse	Legacy remote transport, deprecated in favor of http; no OAuth

Declare the transport explicitly with "type": "http" | "stdio" | "sse" in the server entry. HTTP/SSE servers use url (+ optional headers/oauth); stdio servers use command/args/env.

Tool Search & deferred tools

As of 2026, Claude Code defers MCP tool schemas by default instead of loading every tool's name + description + JSON schema into context up front. Claude discovers tools on demand via the built-in ToolSearch tool, then calls them normally. This is what lets a session connect to dozens of MCP servers (thousands of tools) without drowning the context window.

• Default behavior: a connecting server's tools appear by name only; their schemas load when ToolSearch matches them to the task.
• Force a server's tools to always load (skip deferral): set "alwaysLoad": true on the server entry — use only for small, always-needed servers.
• Disable globally: ENABLE_TOOL_SEARCH=false (rarely worth it — you trade context for eager loading). With deferral off, WaitForMcpServers is available to block until background servers finish connecting.
• Output caps: large tool results are truncated at a default token ceiling; raise it per session with MAX_MCP_OUTPUT_TOKENS.

Implication for this plugin's design: the old "every tool costs context every turn" math is now mostly paid only for alwaysLoad servers and built-ins. Still prefer MCP Prompts/Resources for heavy reference material, but the deferral default means a few extra servers are no longer the liability they once were.

Top recommendations (every project)

Server	Why
context7	Library documentation lookup — always up-to-date
engram (already global)	Persistent memory across sessions
This plugin's MCP (15 docs + 7 KB tools)	Claude Code expertise

Recommendations by stack

Use cc_docs_hook_pack_recommend / cc_docs_team_topology_recommend style logic:

Stack signal	Server
PostgreSQL	@modelcontextprotocol/server-postgres
GitHub Actions / .github/	@modelcontextprotocol/server-github
Playwright config	@playwright/mcp
Sentry DSN	sentry MCP
Slack token	slack MCP
Obsidian vault	Obsidian MCP (Local REST API)

Obsidian MCP — first-class integration

The user's vault is at C:/Users/MarkusAhling/obsidian/. If the Local REST API plugin is installed in Obsidian, expose it via:

{
  "mcpServers": {
    "obsidian": {
      "command": "npx",
      "args": ["-y", "obsidian-mcp-server"],
      "env": { "OBSIDIAN_API_URL": "http://127.0.0.1:27123", "OBSIDIAN_API_KEY": "..." }
    }
  }
}

Claude then reads/writes vault notes via mcp__obsidian__* tools — used extensively by the memory-consolidator (tier 2 writes).

Channels (event-driven MCPs)

Channels are MCP servers that receive external events (webhooks, messages) and expose them to Claude. Four patterns:

Pattern	Use
ci-webhook	Receive GitHub Actions events via webhook with HMAC verification
mobile-approval	Telegram-based permission relay (requires Claude Code v2.1.81+)
discord-bridge	Two-way Discord ↔ Claude with discord_reply tool
fakechat	Built-in local dev channel for testing channel flows

Fetch implementation via cc_kb_channel_server(name) — returns full TypeScript source.

Debugging connection issues

1. Server doesn't start: check stdin/stdout isn't polluted by logging. MCP servers must write logs to stderr only.
2. Server crashes silently: run the command manually (npx -y server-name) to see stderr.
3. Tools not visible to Claude: check capabilities.tools is declared in server init, and ListToolsRequestSchema handler exists.
4. Slow tool calls: check for synchronous file I/O or network calls in hot paths.

MCP delegation

Need	Tool
Fetch channel server code	cc_kb_channel_server(pattern)
Settings schema reference	cc_docs_settings_schema
General MCP troubleshooting	cc_docs_troubleshoot("mcp")

Anti-patterns

• 20+ MCP servers globally → 50k+ tokens passive context cost.
• Putting secrets in .mcp.json → commits leak keys. Use env vars.
• stdin logging in an MCP server → breaks the protocol framing.
• Same MCP server installed globally AND project-scoped → duplicate tool definitions.
• Skipping HMAC verification on webhook channels → anyone can spam your Claude.