Mcp Reap

MCP Reap

Reclaims orphaned Claude Desktop MCP server child processes — leftovers from previously-closed sessions that were never reliably terminated and linger, accumulating RAM. Driven by two hooks so it runs both once per session and periodically thereafter, without requiring a restart:

• hooks/session-start/ss.mcp.reap.js — fires once, every SessionStart.
• hooks/stop/stop.mcp.reap.js — fires on Stop (end of a response

turn), gated by a ~20-minute per-worktree cooldown so it doesn't scan every turn. The cooldown marker uses the same atomic write-temp-then- rename pattern as self-calibration, keyed to an md5 hash of process.cwd() in os.tmpdir().

Both hooks spawn scripts/mcp-reap.js --apply --json detached, fire-and-forget, windowless ({ detached: true, stdio: 'ignore', windowsHide: true } + .unref()) and exit immediately — reaping never delays a session start or a response turn.

Safety model

The scan-and-kill logic lives in hooks/lib/mcp-reaper.js (fully unit tested, 46/46 in mcp-reaper.test.js) and is Windows-only — the dead-parent-PID orphan signal only means anything on Windows, so the module is a documented no-op on macOS/Linux. A process is only ever a reap candidate when it matches an MCP-server launcher signature, its parent PID is confirmed dead, AND it falls outside the live-Claude census (every currently-live claude/claude.exe process plus its full descendant subtree) and the caller's own process subtree — an empty/unbuildable census means "protection unknown" and refuses to produce any candidates at all. Every candidate is re-validated against a fresh process snapshot immediately before both the SIGTERM and any SIGKILL escalation (TOCTOU-safe), so a pid reused for something else between scan and kill is skipped, never touched. The reap() module itself defaults to dry-run — nothing is ever terminated unless a caller explicitly passes --apply; both hooks opt into it deliberately, on the reasoning that a leaked orphan is safe to reclaim automatically once the safety net above holds. Any enumeration or kill failure fails safe (skip, never throw).

Run manually

node scripts/mcp-reap.js               # dry-run, human summary
node scripts/mcp-reap.js --json        # dry-run, JSON output
node scripts/mcp-reap.js --apply       # reclaim now — sofort ohne Neustart
node scripts/mcp-reap.js --apply --json

Every run — including the detached ones spawned by the hooks — persists its result to dotclaude-mcp-reap-status.json in os.tmpdir(), so "what did it reap (or not)?" is inspectable after the fact even though the hooks discard stdout (stdio: 'ignore').

Constraints

• Silent unless it reaps — no console noise on a clean scan, no window ever

(windowless spawn on both the hook side and inside the reaper's own powershell.exe/wmic process-enumeration calls).

• Never blocks session start or a response turn — both hooks are wrapped in

try/catch and always exit 0, even if spawning the detached CLI fails.

• Non-Windows platforms: both hooks Windows-gate cheaply before spawning

anything (the reaper is a no-op there anyway).

• Cooldown degrades safely: if os.tmpdir() is unwritable, the Stop hook's

marker write fails silently and the hook simply fires every turn instead of crashing.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Jerry0022
• Source: Jerry0022/dotclaude
• License: MIT

Install and usage instructions live in the source repository linked above.