memex: capture decision from PR #14

knowledge/decisions/2026-04-10-0935-implement-mcp-server-using-stdio-transport-and-fastmcp.md

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+---
+title: "Implement MCP server using stdio transport and FastMCP SDK for AI agent integration"
+date: 2026-04-10
+author: "Jonasb8"
+source: "https://github.com/Jonasb8/memex/pull/14"
+pr: 14
+repo: "Jonasb8/memex"
+confidence: 0.88
+tags: []
+---
+
+# Implement MCP server using stdio transport and FastMCP SDK for AI agent integration
+
+## Context
+
+The memex CLI already provides semantic search over a local knowledge index for human users, but AI coding agents (Claude Code, Cursor, Copilot, Windsurf) need a different integration path — some cannot run arbitrary bash commands, and all benefit from auto-discoverable tools rather than prompt-based invocation. An MCP (Model Context Protocol) server would expose the knowledge index natively to these agents.
+
+## Decision
+
+Implement a stdio-transport MCP server using the official `mcp` SDK's `FastMCP` class, exposing three tools (`memex_query`, `memex_get_decision`, `memex_list_recent`) that reuse existing CLI functions with no duplication, launchable via `memex serve` or `python -m memex.mcp_server`.
+
+## Alternatives considered
+
+- Network/HTTP transport (rejected in favour of stdio — no port, no persistent process, launched as subprocess by editor)
+- Third-party MCP dependencies (rejected — official `mcp` SDK used instead)
+- Higher default min_score for memex_query (CLI uses 0.7; agents get 0.5 so borderline matches are surfaced with confidence score)
+
+## Constraints
+
+- Must support agents that cannot run arbitrary bash (Cursor, Copilot)
+- No network port or persistent process — must be launchable as a subprocess by the editor
+- Must reuse existing functions from cli.py with zero duplication
+- Early listing in MCP registries is prioritised over completeness
+- Must use official mcp SDK (mcp>=1.0.0), no third-party alternatives
+
+## Revisit signals
+
+- Being listed in MCP registries early matters more than being listed complete — implies feature set may expand later
+
+---
+
+_Extracted by Memex from [PR #14](https://github.com/Jonasb8/memex/pull/14) · 2026-04-10_