diff --git a/scripts/seed-matrix-creds.ts b/scripts/seed-matrix-creds.ts
new file mode 100644
index 0000000..4bb1d94
--- /dev/null
+++ b/scripts/seed-matrix-creds.ts
@@ -0,0 +1,156 @@
+/**
+ * Local helper for seeding the deployed bot's Matrix credentials when the
+ * in-container sniff can't reach an authed /chat/ surface and noVNC isn't
+ * an option (e.g. Dokploy behind a WebSocket-stripping proxy).
+ *
+ * Flow:
+ *   1. Opens a headed Chromium against a throwaway local profile.
+ *   2. You log in to Reddit interactively in that window.
+ *   3. The script navigates to chat.reddit.com and watches for the first
+ *      authed request to matrix.redditspace.com.
+ *   4. The captured bearer is POSTed to the deployed bot's
+ *      /api/debug/matrix-credentials endpoint.
+ *
+ * Usage:
+ *   BOT_URL=https://red.apps.jbrunton.co.uk \
+ *     tsx scripts/seed-matrix-creds.ts
+ *
+ * Optional: PROFILE_DIR=./tmp/seed-session to persist your session across
+ * runs. Otherwise a temp dir is used.
+ */
+
+import fs from 'fs';
+import os from 'os';
+import path from 'path';
+import { chromium, type Request } from 'playwright';
+import { createLogger } from '../src/utils/logger.js';
+import { fetchWithTimeout } from '../src/utils/fetch-with-timeout.js';
+
+const MATRIX_HOST_RE = /matrix\.(redditspace|reddit)\.com$/i;
+
+async function main() {
+  const logger = createLogger();
+  const botUrl = process.env.BOT_URL?.replace(/\/$/, '');
+  if (!botUrl) {
+    logger.error('BOT_URL env var is required (e.g. https://red.apps.jbrunton.co.uk)');
+    process.exit(1);
+  }
+
+  const profileDir =
+    process.env.PROFILE_DIR ??
+    fs.mkdtempSync(path.join(os.tmpdir(), 'reddit-seed-'));
+  logger.info(`[seed] using profile dir: ${profileDir}`);
+
+  logger.info('[seed] launching browser — log in to Reddit in the window that opens');
+  const context = await chromium.launchPersistentContext(profileDir, {
+    headless: false,
+    viewport: { width: 1280, height: 800 },
+  });
+
+  const page = context.pages()[0] ?? (await context.newPage());
+
+  await page.goto('https://www.reddit.com/login', { waitUntil: 'domcontentloaded' });
+  logger.info('[seed] waiting for you to finish login (we watch for /api/me.json success)...');
+
+  // Poll /api/me.json from inside the page until it returns a user — that's
+  // our signal that login (including any 2FA / captcha steps) is complete.
+  const loggedIn = await page.waitForFunction(
+    async () => {
+      try {
+        const r = await fetch('/api/me.json', { credentials: 'include' });
+        if (!r.ok) return false;
+        const j = await r.json();
+        return Boolean(j && j.data && j.data.name);
+      } catch {
+        return false;
+      }
+    },
+    { timeout: 5 * 60_000, polling: 2_000 },
+  ).then(() => true).catch(() => false);
+
+  if (!loggedIn) {
+    logger.error('[seed] gave up waiting for login after 5 minutes');
+    await context.close();
+    process.exit(1);
+  }
+  logger.info('[seed] login detected — opening chat surface to sniff Matrix bearer');
+
+  let captured: { homeserver: string; accessToken: string } | null = null;
+  const onRequest = (request: Request) => {
+    if (captured) return;
+    try {
+      const url = new URL(request.url());
+      if (!MATRIX_HOST_RE.test(url.hostname)) return;
+      const headers = request.headers();
+      const auth = headers['authorization'] || headers['Authorization'];
+      if (!auth || !auth.toLowerCase().startsWith('bearer ')) return;
+      const token = auth.slice('bearer '.length).trim();
+      if (!token) return;
+      captured = { homeserver: `${url.protocol}//${url.host}`, accessToken: token };
+      logger.info(`[seed] captured bearer for ${captured.homeserver}`);
+    } catch {
+      // ignore malformed
+    }
+  };
+  page.on('request', onRequest);
+
+  await page.goto('https://www.reddit.com/chat/', { waitUntil: 'domcontentloaded' });
+  const deadline = Date.now() + 60_000;
+  while (!captured && Date.now() < deadline) {
+    await page.waitForTimeout(500);
+  }
+
+  if (!captured) {
+    logger.error('[seed] did not see any authed matrix.redditspace.com requests after 60s');
+    logger.error('[seed] try clicking around the chat UI in the open browser, then re-run');
+    await context.close();
+    process.exit(1);
+  }
+
+  // Resolve user_id via whoami so the bot has it cached too.
+  let userId = '';
+  try {
+    const r = await fetchWithTimeout(
+      `${captured.homeserver}/_matrix/client/v3/account/whoami`,
+      {
+        headers: { Authorization: `Bearer ${captured.accessToken}` },
+        timeoutMs: 15_000,
+      },
+    );
+    if (r.ok) {
+      const body = (await r.json()) as { user_id?: string };
+      if (body.user_id) userId = body.user_id;
+    }
+  } catch (e) {
+    logger.warn(`[seed] whoami failed (continuing without user_id): ${(e as Error).message}`);
+  }
+
+  const payload = {
+    homeserver: captured.homeserver,
+    accessToken: captured.accessToken,
+    userId,
+    capturedAt: Date.now(),
+  };
+
+  logger.info(`[seed] POSTing credentials to ${botUrl}/api/debug/matrix-credentials`);
+  const res = await fetchWithTimeout(`${botUrl}/api/debug/matrix-credentials`, {
+    method: 'POST',
+    headers: { 'Content-Type': 'application/json' },
+    body: JSON.stringify(payload),
+    timeoutMs: 30_000,
+  });
+  const text = await res.text();
+  if (!res.ok) {
+    logger.error(`[seed] upload failed: ${res.status} ${text}`);
+    await context.close();
+    process.exit(1);
+  }
+  logger.info(`[seed] upload succeeded: ${text}`);
+
+  await context.close();
+}
+
+main().catch((err) => {
+  console.error(err);
+  process.exit(1);
+});
diff --git a/src/services/chat/index.ts b/src/services/chat/index.ts
index de197e9..0e46cd7 100644
--- a/src/services/chat/index.ts
+++ b/src/services/chat/index.ts
@@ -20,5 +20,6 @@ export type { MatrixCredentials } from './matrix/types.js';
 export {
   extractMatrixCredentials,
   loadCachedCredentials,
+  saveCredentials,
 } from './matrix/token-extractor.js';
 export { MatrixMediaDownloader } from './matrix/http-media-downloader.js';
diff --git a/src/web/routes/debug.ts b/src/web/routes/debug.ts
index 2837d46..482ce35 100644
--- a/src/web/routes/debug.ts
+++ b/src/web/routes/debug.ts
@@ -2,6 +2,11 @@ import { Router } from 'express';
 import path from 'path';
 import fs from 'fs';
 import type { WebContext } from '../context.js';
+import {
+  MatrixClient,
+  saveCredentials,
+  type MatrixCredentials,
+} from '../../services/chat/index.js';
 
 export function createDebugRouter(ctx: WebContext): Router {
   const router = Router();
@@ -60,6 +65,40 @@ export function createDebugRouter(ctx: WebContext): Router {
     }
   });
 
+  // Accepts a Matrix credentials JSON body, persists it to the cache file,
+  // and swaps it into the running ChatService. Lets us seed the deployed bot
+  // from a sniff run on a developer's machine when the in-container sniff
+  // can't reach an authed /chat/ surface and noVNC isn't an option.
+  //
+  // Body shape: { homeserver, accessToken, userId?, capturedAt? }
+  router.post('/debug/matrix-credentials', (req, res) => {
+    const body = (req.body ?? {}) as Partial<MatrixCredentials>;
+    if (!body.homeserver || !body.accessToken) {
+      res.status(400).json({ error: 'homeserver and accessToken are required' });
+      return;
+    }
+    const creds: MatrixCredentials = {
+      homeserver: body.homeserver,
+      accessToken: body.accessToken,
+      userId: body.userId ?? '',
+      capturedAt: body.capturedAt ?? Date.now(),
+    };
+    try {
+      saveCredentials(creds);
+      ctx.logger.info(
+        `[matrix] credentials uploaded via /api/debug/matrix-credentials (user=${creds.userId || 'unknown'})`,
+      );
+      if (ctx.services.chat) {
+        ctx.services.chat.setMatrixClient(new MatrixClient(creds, ctx.logger));
+        ctx.logger.info('[matrix] uploaded credentials swapped into running ChatService');
+      }
+      res.json({ success: true, homeserver: creds.homeserver, userId: creds.userId });
+    } catch (error) {
+      ctx.logger.error('Matrix credential upload failed:', error);
+      res.status(500).json({ error: String(error) });
+    }
+  });
+
   router.post('/debug/inspect-dom', async (req, res) => {
     if (!ctx.services.chat) {
       res.status(500).json({ error: 'Chat service not initialized' });