diff --git a/CLAUDE.md b/CLAUDE.md
index 34911b6..5bd0acb 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -42,9 +42,9 @@ Two harness details are load-bearing rather than incidental:
 
 **Memory writes are gated by skill, per turn.** A file-tool write into `.claude/memories/` is denied unless a memory skill authorizes it. A Bash `rm`, `unlink`, `mv` or `git rm` whose command mentions `memories` is denied unless memory-audit ran, because only the audit deletes, and only after per-batch approval. That check exists for auto mode, where no permission prompt would stop the command. It matches the whole command rather than parsing arguments, since variables, globs and `cd` make parsing easy to evade. The scope is the turn for capture because a session that loaded the skill turns earlier edits from a stale copy and skips its checks. A typed skill command produces no `Skill` tool call, only prompt text, which is why the `UserPromptSubmit` branch scans the prompt as well. This gate ignores `KB_GATE_MODE` except `off`, so its own per-turn denial budget is what keeps a broken `Skill` record from blocking writes forever.
 
-**Both hooks fail open.** Unexpected filesystem or payload errors exit 0 without output. The gate never exits 2, never calls qmd, and logs every evaluation except when disabled or when an uninteresting sub-agent starts. Preserve the append-only query and denial files, monotonic turn counter, and separate per-state/per-turn denial budgets. Gate state is compatible with previous shell installs.
+**Both hooks fail open.** Unexpected filesystem or payload errors exit 0 without output. The gate never exits 2, never calls qmd, and logs every evaluation except when disabled, when the project has opted out, or when an uninteresting sub-agent starts. Preserve the append-only query and denial files, monotonic turn counter, and separate per-state/per-turn denial budgets. Gate state is compatible with previous shell installs.
 
-**Project-root derivation must agree everywhere.** `hooks/shared.mts` resolves git toplevel → `CLAUDE_PROJECT_DIR` → `$PWD` for the hooks. The small shell launchers and doctor checks in `techpack.yaml` retain the same ladder. Keep those shell copies identical to one another and behaviorally equivalent to the TypeScript helper. All readers and writers use `.claude/.kb-index/`. Tests exercise git subdirectories, non-git fallbacks, and paths needing YAML escaping.
+**Project-root derivation must agree everywhere.** `hooks/shared.mts` resolves git toplevel → `CLAUDE_PROJECT_DIR` → `$PWD` for the hooks. The small shell launchers and doctor checks in `techpack.yaml` retain the same ladder. Keep those shell copies identical to one another and behaviorally equivalent to the TypeScript helper. All readers and writers use `.claude/.kb-index/`. Tests exercise git subdirectories, non-git fallbacks, and paths needing YAML escaping. Every hook does nothing when `.claude/.no-memory-loop` exists at that root (`optedOut` in TypeScript, a copy of the ladder in `hooks/memory-loop-activator.sh`), so a new entry point needs the check too.
 
 **Indexing is unconditional and incremental.** qmd handles added, edited, deleted, and symlinked memories. Do not add a separate staleness check. The config stores the literal memories path, repairs drift, and is written even before the first memory exists. The directory lock protects update/embed/status/cleanup, and stale empty locks are reclaimed using the previous `find -mmin +5` age rule.
 
diff --git a/README.md b/README.md
index 67ba6a2..f6b24df 100644
--- a/README.md
+++ b/README.md
@@ -110,6 +110,10 @@ Writes to `.claude/memories/` are gated separately, and in every mode except `of
 
 To change the mode, run `mcs sync` again. The selection is baked into the installed hook rather than read from a runtime setting.
 
+## Opting a project out
+
+To exclude one project from a global install, create `.claude/.no-memory-loop` in its root yourself; the gate stops an agent from creating or removing it. The hooks then do nothing there. The MCP server is still registered, so deny it in that project's settings (`"permissions": { "deny": ["mcp__memory-loop"] }`).
+
 ## What's included
 
 | Component | What it does |
diff --git a/hooks/kb-gate.mts b/hooks/kb-gate.mts
index 8c45a1d..b070b03 100755
--- a/hooks/kb-gate.mts
+++ b/hooks/kb-gate.mts
@@ -12,7 +12,7 @@ import {
   writeFileSync,
 } from "node:fs";
 import { basename, dirname, join, resolve } from "node:path";
-import { attempt, isDirectory, projectRoot, read } from "./shared.mts";
+import { attempt, isDirectory, OPT_OUT_MARKER, optedOut, projectRoot, read } from "./shared.mts";
 
 const MODE: string = "__KB_GATE_MODE__";
 const MAX_DENIALS_PER_STATE = 4;
@@ -132,13 +132,30 @@ function gate(): void {
   const isRetrieval = event === "PostToolUse" && RETRIEVAL_TOOLS.includes(payload.tool_name);
   const isMemoryWrite = event === "PreToolUse" && MEMORY_WRITE_TOOLS.includes(payload.tool_name);
   const target = payload.tool_input?.file_path || payload.tool_input?.notebook_path || "";
-  if (target && !mentionsMemories(target)) return;
   const command = String(payload.tool_input?.command ?? "");
+  // The marker also switches off the memory write gate, so an agent must not be able to set or clear it.
+  if (
+    event === "PreToolUse" &&
+    ((isMemoryWrite && basename(target) === OPT_OUT_MARKER) || (payload.tool_name === "Bash" && command.includes(OPT_OUT_MARKER)))
+  ) {
+    process.stdout.write(
+      `${JSON.stringify({
+        hookSpecificOutput: {
+          hookEventName: event,
+          permissionDecision: "deny",
+          permissionDecisionReason: `Only the user opts a project in or out of the memory loop. Ask them to create or remove .claude/${OPT_OUT_MARKER} themselves.`,
+        },
+      })}\n`,
+    );
+    return;
+  }
+  if (target && !mentionsMemories(target)) return;
   const isMemoryDelete =
     event === "PreToolUse" && payload.tool_name === "Bash" && command.includes("memories") && MEMORY_DELETE.test(command);
   if (event === "PreToolUse" && payload.tool_name === "Bash" && !isMemoryDelete) return;
 
   const root = projectRoot();
+  if (optedOut(root)) return;
   const memories = `${root}/.claude/memories`;
   const usage = `${memories}/.usage.tsv`;
   const state = `${root}/.claude/.kb-gate`;
diff --git a/hooks/memory-loop-activator.sh b/hooks/memory-loop-activator.sh
index d07545c..a07b291 100644
--- a/hooks/memory-loop-activator.sh
+++ b/hooks/memory-loop-activator.sh
@@ -1,5 +1,9 @@
 #!/bin/bash
 
+r=$(git rev-parse --show-toplevel 2>/dev/null)
+[ -n "$r" ] || r="${CLAUDE_PROJECT_DIR:-$PWD}"
+[ -e "$r/.claude/.no-memory-loop" ] && exit 0
+
 cat << 'EOF'
 Memory: search the KB before a new phase, and on an unexpected error
 before diagnosing it from scratch. Before your final reply, run
diff --git a/hooks/shared.mts b/hooks/shared.mts
index 5f52800..6e68c4e 100644
--- a/hooks/shared.mts
+++ b/hooks/shared.mts
@@ -1,5 +1,5 @@
 import { spawnSync } from "node:child_process";
-import { accessSync, constants, readFileSync, statSync } from "node:fs";
+import { accessSync, constants, existsSync, readFileSync, statSync } from "node:fs";
 import { delimiter, join } from "node:path";
 
 export function attempt<T>(action: () => T): T | undefined {
@@ -33,3 +33,9 @@ export function projectRoot(): string {
   const result = spawnSync("git", ["rev-parse", "--show-toplevel"], { encoding: "utf8", stdio: ["ignore", "pipe", "ignore"] });
   return result.stdout?.replace(/\n+$/, "") || process.env.CLAUDE_PROJECT_DIR || process.env.PWD || process.cwd();
 }
+
+export const OPT_OUT_MARKER = ".no-memory-loop";
+
+export function optedOut(root: string): boolean {
+  return existsSync(`${root}/.claude/${OPT_OUT_MARKER}`);
+}
diff --git a/hooks/sync-memories.mts b/hooks/sync-memories.mts
index 97ceeb5..0897eb5 100755
--- a/hooks/sync-memories.mts
+++ b/hooks/sync-memories.mts
@@ -1,13 +1,14 @@
 #!/usr/bin/env -S node --experimental-strip-types --disable-warning=ExperimentalWarning
 import { spawnSync } from "node:child_process";
 import { closeSync, mkdirSync, openSync, renameSync, rmdirSync, rmSync, statSync, writeFileSync } from "node:fs";
-import { attempt, commandExists, isDirectory, projectRoot, read } from "./shared.mts";
+import { attempt, commandExists, isDirectory, optedOut, projectRoot, read } from "./shared.mts";
 
 const embedModel = "hf:Qwen/Qwen3-Embedding-0.6B-GGUF/Qwen3-Embedding-0.6B-Q8_0.gguf";
 
 function syncMemories(): void {
   attempt(() => read(0));
   const root = projectRoot();
+  if (optedOut(root)) return;
   const memories = `${root}/.claude/memories`;
   const directory = `${root}/.claude/.kb-index`;
   const config = `${directory}/memory-loop.yml`;
diff --git a/tests/contracts.test.mts b/tests/contracts.test.mts
index bf92038..754a84b 100644
--- a/tests/contracts.test.mts
+++ b/tests/contracts.test.mts
@@ -25,6 +25,12 @@ test("hook messages match the original shell output byte for byte", t => {
   assert.equal(f.run(`${root}/hooks/memory-loop-activator.sh`), messages.activator);
 });
 
+test("the activator is silent in an opted-out project", t => {
+  const f = fixture(t);
+  f.optOut();
+  assert.equal(f.run(`${root}/hooks/memory-loop-activator.sh`), "");
+});
+
 test("no two hook components share an event and destination", () => {
   const registrations = hooks.map(component => `${field(component, "hookEvent")} ${field(component, "destination")}`);
   assert.deepEqual(registrations, [...new Set(registrations)], "mcs keeps one registration per event and command");
diff --git a/tests/helpers.mts b/tests/helpers.mts
index 6c3e8eb..20d9587 100644
--- a/tests/helpers.mts
+++ b/tests/helpers.mts
@@ -44,7 +44,8 @@ export function fixture(t: TestContext) {
       assert.equal(result.stderr, "");
       return result.stdout;
     });
-  return { work, project, env, run, runAsync };
+  const optOut = () => writeFileSync(`${project}/.claude/.no-memory-loop`, "");
+  return { work, project, env, run, runAsync, optOut };
 }
 
 export function gateFixture(t: TestContext, mode = "enforce") {
diff --git a/tests/kb-gate.test.mts b/tests/kb-gate.test.mts
index 76d0ea4..908da63 100644
--- a/tests/kb-gate.test.mts
+++ b/tests/kb-gate.test.mts
@@ -108,6 +108,31 @@ test("discovery agents receive the same briefing and marker as the template", t
   assert.equal(f.event("SubagentStart", { agent_type: "Explore" }), "");
 });
 
+test("an opted-out project is never gated, briefed or logged", t => {
+  const f = gateFixture(t);
+  f.optOut();
+  f.turn();
+  assert.equal(f.spawn(), "");
+  assert.equal(f.event("SubagentStart", { agent_type: "Explore" }), "");
+  assert.equal(f.write(), "");
+  f.memories("learning_x.md");
+  f.retrieve(["learning_x.md"]);
+  assert.equal(existsSync(f.usagePath), false);
+  assert.equal(existsSync(f.state), false);
+  assert.equal(existsSync(f.log), false);
+});
+
+test("agents can neither set nor clear the opt-out marker", t => {
+  const f = gateFixture(t);
+  const marker = `${f.project}/.claude/.no-memory-loop`;
+  denied(f.write({ file_path: marker }));
+  denied(f.bash(`touch ${marker}`));
+  f.optOut();
+  denied(f.bash(`rm ${marker}`));
+  denied(f.write({ file_path: marker, agent_id: "agent" }));
+  assert.equal(f.bash("ls"), "");
+});
+
 test("malformed payloads fail open without output or state", t => {
   const f = gateFixture(t);
   for (const payload of ["", "{", "null", "42", "[]", { tool_input: { prompt: 4 } }, { hook_event_name: "unknown" }]) {
diff --git a/tests/sync-memories.test.mts b/tests/sync-memories.test.mts
index 1af4171..37543a5 100644
--- a/tests/sync-memories.test.mts
+++ b/tests/sync-memories.test.mts
@@ -51,6 +51,13 @@ for (const linked of [false, true]) {
   });
 }
 
+test("an opted-out project is neither configured nor indexed", t => {
+  const f = indexer(t);
+  f.optOut();
+  assert.deepEqual(f.run(), []);
+  assert.equal(existsSync(f.directory), false);
+});
+
 test("config is registered before memories exist, repaired on drift, and stable otherwise", t => {
   const f = indexer(t);
   rmSync(`${f.project}/.claude/memories`, { recursive: true });