diff --git a/CHANGELOG.md b/CHANGELOG.md
index 463590a..ad6e95a 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+
+### Documentation
+- Added a troubleshooting guide for backend connection, Android permissions, model configuration, and local Redis/PostgreSQL conflicts.
 ## [0.1.0] - 2026-03-30
 
 ### Initial source-available release
diff --git a/README.md b/README.md
index f70b5c9..47221d0 100644
--- a/README.md
+++ b/README.md
@@ -16,6 +16,7 @@
 
 ## Recent Updates
 
+- `[2026.5.12]` Added a troubleshooting guide for backend connection, Android permissions, model configuration, and local Redis/PostgreSQL conflicts.
 - `[2026.5.9]` Added a Discord IM channel for remote Android task dispatch, including prefix commands, slash commands, allowlists, and guild-scoped command registration.
 - `[2026.5.7]` Hardened local startup to avoid common PostgreSQL and Redis port conflicts during Docker-based backend setup.
 - `[2026.5.1]` Improved backend onboarding with `.env.example`, startup checks, and graph-agent VLM environment configuration.
@@ -146,6 +147,7 @@ cd client
 Reference docs:
 
 - [docs/get-started.md](./docs/get-started.md)
+- [docs/troubleshooting.md](./docs/troubleshooting.md)
 - [server/start.sh](./server/start.sh)
 - [client/start.sh](./client/start.sh)
 - [server/apps/backend/README.md](./server/apps/backend/README.md)
diff --git a/docs/troubleshooting.md b/docs/troubleshooting.md
new file mode 100644
index 0000000..e484dbc
--- /dev/null
+++ b/docs/troubleshooting.md
@@ -0,0 +1,150 @@
+# Troubleshooting
+
+Use this guide when the backend starts but the Android client cannot run a task, report progress, or keep the device ready for remote work.
+
+## Backend connection
+
+### Android client cannot reach the backend
+
+Likely causes:
+
+- the backend is not running
+- the Android client is using the wrong server URL
+- the backend is bound to `localhost` only
+- a firewall blocks the backend port
+
+Checks:
+
+```bash
+cd server
+./start.sh
+```
+
+Open the backend health or API endpoint from the host machine first. Then open the same address from the Android device browser.
+
+Fixes:
+
+- use the host machine LAN IP instead of `localhost` when connecting from a physical phone
+- make sure the phone and host machine are on the same network
+- allow the backend port through the host firewall
+- restart the Android client after changing the server URL
+
+### Emulator uses the wrong host address
+
+Android emulators do not use `localhost` to reach the host machine.
+
+Use:
+
+```text
+http://10.0.2.2:<backend-port>
+```
+
+For Genymotion or other emulator runtimes, check the runtime-specific host gateway address.
+
+### Physical phone cannot connect to the laptop backend
+
+Checks:
+
+- confirm the phone and laptop are on the same Wi-Fi network
+- confirm VPN, guest Wi-Fi, or hotspot isolation is not blocking local traffic
+- open `http://<laptop-lan-ip>:<backend-port>` from the phone browser
+- confirm the backend is listening on all interfaces, not only `127.0.0.1`
+
+Fixes:
+
+- use the laptop LAN IP in the Android client server URL
+- disable guest network isolation or move both devices to the same trusted network
+- allow inbound traffic for the backend port in Windows Defender Firewall, macOS firewall, or Linux firewall rules
+
+## Android permissions
+
+### AccessibilityService is disabled or killed
+
+Symptoms:
+
+- tasks start but no taps, swipes, or text input happen
+- screenshots work but UI actions do not execute
+- the service disappears after the screen is locked or the app is backgrounded
+
+Checks:
+
+- Android Settings -> Accessibility -> OpenGUI service is enabled
+- the Android client is allowed to run in the background
+- battery optimization is disabled for the Android client
+
+Fixes:
+
+- re-enable the AccessibilityService after installing a new APK
+- disable battery optimization for the Android client
+- keep the device unlocked during local debugging
+- check vendor-specific background app settings on Xiaomi, Huawei, Oppo, Vivo, Samsung, and similar devices
+
+### Overlay permission blocks task feedback
+
+Symptoms:
+
+- the client runs but progress UI or floating task feedback never appears
+- Android shows a permission warning for displaying over other apps
+
+Fixes:
+
+- Android Settings -> Apps -> OpenGUI -> Display over other apps -> Allow
+- restart the client after granting the permission
+- on restricted devices, grant the permission through the vendor security or permission manager app
+
+## Model configuration
+
+### Missing model API configuration
+
+Symptoms:
+
+- backend starts but planning or vision steps fail
+- task output mentions missing provider credentials
+- requests fail immediately before any Android action
+
+Checks:
+
+- compare local environment variables with `.env.example`
+- confirm the provider API key is present
+- confirm the selected model supports the role it is assigned to
+
+Fixes:
+
+- fill in the required model provider keys before starting the backend
+- restart the backend after changing environment variables
+- start with one known working provider profile, then split planner and vision models after the first successful run
+
+## Local services
+
+### Redis or PostgreSQL port conflicts
+
+Symptoms:
+
+- `./start.sh` fails before the backend is ready
+- logs mention a port already in use
+- Docker starts some services but not Redis or PostgreSQL
+
+Checks:
+
+```bash
+docker ps
+docker compose ps
+```
+
+Fixes:
+
+- stop the local service that already uses the same port
+- update the project environment or compose port mapping to use a free port
+- restart the backend after changing service ports
+
+## Reporting a useful issue
+
+If the problem still happens, include:
+
+- host operating system
+- Android device or emulator type
+- Android version
+- backend server URL used by the client, with secrets removed
+- the exact symptom and the first failing step
+- relevant backend logs
+- whether AccessibilityService, overlay permission, and battery settings were enabled