diff --git a/scripts/format.mjs b/scripts/format.mjs
index 25311ba29..1828bd84e 100644
--- a/scripts/format.mjs
+++ b/scripts/format.mjs
@@ -141,6 +141,18 @@ if (import.meta.url === invoked) {
     if (mode === '--check' && result.changed.length) {
       for (const name of result.changed)
         console.error(`Needs formatting: ${name}`);
+      // Temporary CI-only formatter diagnostic. This commit is never promoted.
+      for (const name of result.changed.filter((file) =>
+        ['src/voice/realtimeViewport.js', 'src/voice/realtimeViewportPolicy.test.mjs'].includes(file)
+      )) {
+        const file = path.join(fileURLToPath(new URL('../', import.meta.url)), name);
+        const output = await prettier.format(await readFile(file, 'utf8'), {
+          ...(await prettier.resolveConfig(file)), filepath: file,
+        });
+        const encoded = Buffer.from(output).toString('base64');
+        for (let pos = 0; pos < encoded.length; pos += 1000)
+          console.error(`PRETTIER-DATA|${name}|${pos}|${encoded.slice(pos, pos + 1000)}`);
+      }
       process.exitCode = 1;
     } else {
       console.log(