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dev-backbone-template/SKILLS/82-mcp-server-design.md
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# MCP Server Design (Agent-First)
Build MCP servers like youre designing a UI for a non-human user.
This skill distills Phil Schmids MCP server best practices into concrete repo rules.
Source: “MCP is Not the Problem, Its your Server” (Jan 21, 2026).
## 1) Outcomes, not operations
- Do **not** wrap REST endpoints 1:1 as tools.
- Expose high-level, outcome-oriented tools.
- Bad: `get_user`, `list_orders`, `get_order_status`
- Good: `track_latest_order(email)` (server orchestrates internally)
## 2) Flatten arguments
- Prefer top-level primitives + constrained enums.
- Avoid nested `dict`/config objects (agents hallucinate keys).
- Defaults reduce decision load.
## 3) Instructions are context
- Tool docstrings are *instructions*:
- when to use the tool
- argument formatting rules
- what the return means
- Error strings are also context:
- return actionable, self-correcting messages (not raw stack traces)
## 4) Curate ruthlessly
- Aim for **515 tools** per server.
- One server, one job. Split by persona if needed.
- Delete unused tools. Dont dump raw data into context.
## 5) Name tools for discovery
- Avoid generic names (`create_issue`).
- Prefer `{service}_{action}_{resource}`:
- `velociraptor_run_hunt`
- `github_list_prs`
- `slack_send_message`
## 6) Paginate large results
- Always support `limit` (default ~2050).
- Return metadata: `has_more`, `next_offset`, `total_count`.
- Never return hundreds of rows unbounded.
## Repo conventions
- Put MCP tool specs in `mcp/` (schemas, examples, fixtures).
- Provide at least 1 “golden path” example call per tool.
- Add an eval that checks:
- tool names follow discovery convention
- args are flat + typed
- responses are concise + stable
- pagination works