diff --git a/scripts/format.mjs b/scripts/format.mjs
index 25311ba29..1ba08abc1 100644
--- a/scripts/format.mjs
+++ b/scripts/format.mjs
@@ -141,6 +141,20 @@ if (import.meta.url === invoked) {
     if (mode === '--check' && result.changed.length) {
       for (const name of result.changed)
         console.error(`Needs formatting: ${name}`);
+      // Temporary formatter output probe for the existing #880 test only.
+      if (result.changed.includes('src/agent/worldPacket.test.mjs')) {
+        const file = path.join(
+          fileURLToPath(new URL('../', import.meta.url)),
+          'src/agent/worldPacket.test.mjs',
+        );
+        const formatted = await prettier.format(await readFile(file, 'utf8'), {
+          ...(await prettier.resolveConfig(file)),
+          filepath: file,
+        });
+        const encoded = Buffer.from(formatted).toString('base64');
+        for (let offset = 0; offset < encoded.length; offset += 1000)
+          console.error(`PRETTIER-DATA|src/agent/worldPacket.test.mjs|${offset}|${encoded.slice(offset, offset + 1000)}`);
+      }
       process.exitCode = 1;
     } else {
       console.log(