diff --git a/docs/architecture/performance-journeys.md b/docs/architecture/performance-journeys.md
index 163e7dba2..4fbd9449a 100644
--- a/docs/architecture/performance-journeys.md
+++ b/docs/architecture/performance-journeys.md
@@ -1228,7 +1228,9 @@ that file:
   `journeys.<journey>.counters` and a wall-clock entry (one with
   `toleranceRatio`) only from `journeys.<journey>.wallClock`, so a value in
   the wrong section also counts as missing;
-- a measurement below its baseline passes and prints a "tighten" hint;
+- a measurement below its baseline passes and prints a "tighten" hint,
+  except for an entry with `"autoTighten": false`, whose band one low run
+  does not move;
 - a measured counter without a baseline is noted, not failed;
 - checking nothing fails: an empty baselines file, or `--only` naming an
   entry that does not exist, cannot exit 0;
diff --git a/tools/performance/check-journey-ratchet.mjs b/tools/performance/check-journey-ratchet.mjs
index 20bf9da0d..370deadae 100644
--- a/tools/performance/check-journey-ratchet.mjs
+++ b/tools/performance/check-journey-ratchet.mjs
@@ -12,6 +12,8 @@
  *   never silently disable the ratchet.
  * - A measurement below its baseline prints a "can tighten" hint. Baselines
  *   are lowered by hand, with the measured output as evidence, never raised.
+ *   An entry with `"autoTighten": false` gets no hint: its slack covers a band
+ *   of normal values, so one low run is no evidence for a lower `value`.
  * - Checking nothing is a failure: an empty baselines file, or `--only`
  *   naming an entry that does not exist, must not exit 0.
  * - An optional `note` (a string) says why an entry is enforced, such as a
@@ -208,6 +210,10 @@ export function compareToBaselines({ baselines, summary, only = [] }) {
                 result.passed.push(
                     `${label}: ${formatNumber(measured)}${unit} within ${limitText}; uses ${formatNumber(measured - entry.value)} of ${formatNumber(limit - entry.value)}${unit} slack.`
                 );
+            } else if (measured < entry.value && entry.autoTighten === false) {
+                result.passed.push(
+                    `${label}: ${formatNumber(measured)}${unit} within ${limitText}; below the baseline, but autoTighten is false: lower it by hand only when the top of its band fell too (docs/architecture/performance-journeys.md).`
+                );
             } else if (measured < entry.value) {
                 result.tightenable.push(
                     `${label}: ${formatNumber(measured)}${unit} is below baseline ${formatNumber(entry.value)} by ${formatNumber(entry.value - measured)}${unit}. Lower the baseline in ${DEFAULT_BASELINES_PATH} with this run as evidence.`
diff --git a/tools/performance/check-journey-ratchet.test.mjs b/tools/performance/check-journey-ratchet.test.mjs
index 4d0386b13..a424ae0de 100644
--- a/tools/performance/check-journey-ratchet.test.mjs
+++ b/tools/performance/check-journey-ratchet.test.mjs
@@ -151,6 +151,42 @@ test('a counter with slack passes up to value + slack and reports the slack used
     assert.match(below.tightenable[0], /below baseline 1,000 by 10 bytes/);
 });
 
+test('an entry with autoTighten false gets no tightening hint below its value', () => {
+    const baselines = {
+        version: 1,
+        journeys: {
+            playback: {
+                'renderer.domMutationsToPlaying': {
+                    value: 733,
+                    unit: 'mutations',
+                    slack: 20,
+                    autoTighten: false,
+                },
+            },
+        },
+    };
+    const result = compareToBaselines({
+        baselines,
+        summary: {
+            journeys: {
+                playback: {
+                    counters: { 'renderer.domMutationsToPlaying': 731 },
+                },
+            },
+        },
+    });
+    assert.deepEqual(result.failures, []);
+    assert.deepEqual(result.tightenable, []);
+    assert.match(
+        result.passed[0],
+        /731 mutations within 753 .*autoTighten is false: lower it by hand/
+    );
+    assert.match(
+        formatResult(result),
+        /1 baselines checked, 0 can be tightened/
+    );
+});
+
 test('wall-clock entries fail only above value × toleranceRatio', () => {
     const within = compareToBaselines({
         baselines,