diff --git a/lib/printer.js b/lib/printer.js
index 75aaea3..19965ae 100644
--- a/lib/printer.js
+++ b/lib/printer.js
@@ -9,8 +9,12 @@ const mqtt = require('mqtt');
 
 const PORT = 8883;
 
+// An id the printer sends as all zeros means no RFID tag was read.
+const realId = (v) => (v && !/^0+$/.test(String(v)) ? String(v) : null);
+
 // One tray, as the printer describes it. `remain` is a percentage; the printer
-// sends -1 when it can't tell, which is mostly the case for non-Bambu spools.
+// sends -1 when it can't tell. An AMS lite only knows full or empty, so its
+// figure isn't a measurement — callers decide whether to trust it.
 function describeTray(tray, unit = null) {
   const loaded = Boolean(tray && tray.tray_type);
   return {
@@ -22,6 +26,10 @@ function describeTray(tray, unit = null) {
     profile: loaded ? tray.tray_info_idx || null : null, // Bambu's filament profile, e.g. GFA00
     brand: loaded ? tray.tray_sub_brands || null : null,
     remain: loaded && Number(tray.remain) >= 0 ? Number(tray.remain) : null,
+    // A Bambu spool's RFID tag: tray_uuid names the spool, tag_uid the tag.
+    uuid: loaded ? realId(tray.tray_uuid) : null,
+    tagUid: loaded ? realId(tray.tag_uid) : null,
+    idName: loaded ? tray.tray_id_name || null : null, // e.g. "A00-W1", on firmware that sends it
   };
 }
 
@@ -45,10 +53,12 @@ function friendlyError(err) {
 
 // Connects, asks for a full report, and gathers what arrives for a few seconds.
 // Resolves with what was seen — never with the access code.
-function probe({ host, serial, accessCode, waitMs = 8000 }) {
+// With `debug`, also returns one loaded tray exactly as the printer sent it, to
+// see which fields a given printer and firmware actually provide.
+function probe({ host, serial, accessCode, waitMs = 8000, debug = false }) {
   return new Promise((resolve) => {
     const started = Date.now();
-    const seen = { connected: false, reports: 0, printer: null, ams: null, external: null, error: null };
+    const seen = { connected: false, reports: 0, printer: null, ams: null, external: null, error: null, raw: null };
     let done = false;
     let timer = null;
     const client = mqtt.connect(`mqtts://${host}:${PORT}`, {
@@ -85,7 +95,18 @@ function probe({ host, serial, accessCode, waitMs = 8000 }) {
       if (!p) return;
       if (p.gcode_state) seen.printer = { ...(seen.printer || {}), state: p.gcode_state };
       if (p.mc_percent != null) seen.printer = { ...(seen.printer || {}), progress: Number(p.mc_percent) };
-      if (p.ams && Array.isArray(p.ams.ams)) seen.ams = describeAms(p.ams.ams);
+      if (p.ams && Array.isArray(p.ams.ams)) {
+        seen.ams = describeAms(p.ams.ams);
+        if (debug) {
+          const unit = p.ams.ams[0] || {};
+          seen.raw = {
+            amsKeys: Object.keys(p.ams),
+            unitKeys: Object.keys(unit),
+            unitInfo: { info: unit.info, humidity: unit.humidity, temp: unit.temp },
+            tray: (unit.tray || []).find((t) => t && t.tray_type) || null,
+          };
+        }
+      }
       if (p.vt_tray) seen.external = describeTray(p.vt_tray, null);
     });
     client.on('error', (err) => {
diff --git a/server.js b/server.js
index 4dcda4b..69f467b 100644
--- a/server.js
+++ b/server.js
@@ -337,7 +337,10 @@ app.post('/api/printer/test', async (req, res, next) => {
     const accessCode = (await resolveSetting('printer_access_code')).value;
     const missing = [!host && 'address', !serial && 'serial number', !accessCode && 'access code'].filter(Boolean);
     if (missing.length) return res.status(400).json({ error: `Fill in the printer’s ${missing.join(', ')} first.` });
-    res.json(await printer.probe({ host: host.trim(), serial: serial.trim(), accessCode: accessCode.trim() }));
+    res.json(await printer.probe({
+      host: host.trim(), serial: serial.trim(), accessCode: accessCode.trim(),
+      debug: req.query.debug === '1', // raw fields for one tray — filament data, no credentials
+    }));
   } catch (e) { next(e); }
 });
 
diff --git a/test/printer.test.js b/test/printer.test.js
index 08fd165..f1f5fb2 100644
--- a/test/printer.test.js
+++ b/test/printer.test.js
@@ -10,7 +10,7 @@ test('AMS trays are read into material, colour and how much is left', () => {
   ] }]);
   assert.deepEqual(trays[0], {
     unit: 0, slot: 0, empty: false, material: 'PLA', colour: '#FFFFFF',
-    profile: 'GFA00', brand: 'PLA Basic', remain: 82,
+    profile: 'GFA00', brand: 'PLA Basic', remain: 82, uuid: null, tagUid: null, idName: null,
   });
   assert.equal(trays[1].empty, true);
   assert.equal(trays[1].material, null);
@@ -19,6 +19,24 @@ test('AMS trays are read into material, colour and how much is left', () => {
   assert.equal(trays[2].colour, '#000000', 'the alpha byte is dropped');
 });
 
+test('a Bambu spool’s RFID identity is kept, and an unread tag is not invented', () => {
+  const [tagged] = printer.describeAms([{ id: '0', tray: [{
+    id: '0', tray_type: 'PLA', tray_color: 'C12E1FFF',
+    tray_uuid: 'A1B2C3D4E5F60718293A4B5C6D7E8F90', tag_uid: '04AB12CD34EF5680', tray_id_name: 'A00-R0',
+  }] }]);
+  assert.equal(tagged.uuid, 'A1B2C3D4E5F60718293A4B5C6D7E8F90');
+  assert.equal(tagged.tagUid, '04AB12CD34EF5680');
+  assert.equal(tagged.idName, 'A00-R0');
+
+  const [plain] = printer.describeAms([{ id: '0', tray: [{
+    id: '0', tray_type: 'PLA', tray_color: 'FFFFFFFF',
+    tray_uuid: '00000000000000000000000000000000', tag_uid: '0000000000000000',
+  }] }]);
+  assert.equal(plain.uuid, null, 'all zeros means no tag was read');
+  assert.equal(plain.tagUid, null);
+  assert.equal(plain.idName, null);
+});
+
 test('a printer with no AMS reports nothing rather than failing', () => {
   assert.deepEqual(printer.describeAms(undefined), []);
   assert.deepEqual(printer.describeAms([{ id: '0' }]), []);