diff --git a/docs/reference/controller.md b/docs/reference/controller.md
new file mode 100644
index 0000000..b02b1fb
--- /dev/null
+++ b/docs/reference/controller.md
@@ -0,0 +1,58 @@
+# FieldPOC controller
+
+The FieldPOC controller is an interactive console to help managing the current state of the FieldPOC system.
+
+Connect to it via the IP address von port set in the [FieldPOC configuration](configuration.md) with `telnet`.
+
+## Commands
+
+### Help
+
+`help`
+
+Show help info.
+
+### Show handlers
+
+`handlers`
+
+Show currently running handlers
+
+### Reconfigure all components
+
+`sync`
+
+Notify all parts of FieldPOC to check configuration of connected components and update it.
+
+### Show queue stats
+
+`queues`
+
+### Reload configuration
+
+`reload`
+
+Read [FieldPOC configuration](configuration.md) file and apply it.
+
+### Bind extension to DECT device
+
+`claim <ext> <token>`
+
+- `ext` is the current extension number of the DECT device.
+- `token` is the `dect_claim_token` of the extension that should get applied.
+
+This works because newly connected DECT phones get a temporary number assigned.
+This temporary number is usually the current number.
+But it is possible to use any extension, so the extension for a device can be changed any time.
+
+### Disconnect
+
+`exit`
+
+Disconnect telnet session.
+
+### Stop controller
+
+`stop`
+
+Shutdown the controller, but FieldPOC continues running.
diff --git a/docs/reference/extensions.md b/docs/reference/extensions.md
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index 0000000..e02f259
--- /dev/null
+++ b/docs/reference/extensions.md
@@ -0,0 +1,100 @@
+# Extensions data
+
+`extensions.json` contains all extension a FieldPOC instance provides.
+
+## Example
+
+```
+{
+  "extensions": {
+    "2574": {
+      "name": "clerie",
+      "type": "dect",
+      "trunk": false,
+      "dialout_allowed": true,
+      "dect_claim_token": "2574"
+    },
+    "5375": {
+      "name": "n0emis",
+      "type": "callgroup",
+      "dialout_allowed": true,
+      "trunk": false,
+      "callgroup_members": [
+        "5376",
+        "5377",
+        "5379"
+      ]
+    },
+    "5376": {
+      "name": "n0emis SIP",
+      "type": "sip",
+      "dialout_allowed": true,
+      "trunk": false,
+      "outgoing_extension": "5375",
+      "sip_password": "wieK5xal"
+    },
+    "5377": {
+      "name": "n0emis DECT",
+      "type": "dect",
+      "dialout_allowed": true,
+      "trunk": false,
+      "outgoing_extension": "5375",
+      "dect_ipei": "10345 0136625 3"
+    },
+    "9998": {
+      "name": "Temporary Numbers",
+      "trunk": false,
+      "dialout_allowed": true,
+      "type": "temp"
+    },
+    "9997": {
+      "name": "DECT Claim Extensions",
+      "type": "static",
+      "dialout_allowed": false,
+      "trunk": true,
+      "static_target": "external/nodata//run/current-system/sw/bin/dect_claim"
+    }
+  }
+}
+
+```
+
+## Extensions definition
+
+The key for an extension is always the number of the extension.
+
+Following keys are required:
+
+- `name`: Description of the extension.
+- `type`: Type of the extension.
+
+## Extension types
+
+Based on the type of the extension more options are required.
+
+### SIP extension
+
+- `type`: `sip`
+- `sip_password`: Plain text password for the SIP account.
+
+### DECT extension
+
+- `type`: `dect`
+- `dect_claim_token`: Phone number part used to connect a DECT phone to this extension.
+- `dect_ipei`: IPEI of the DECT phone this extension should be connected to.
+
+`dect_claim_token` and `dect_ipei` are mutally exclusive.
+
+### Static extension
+
+- `type`: `static`
+- `static_target`: Path to script that is executed on calling this extension.
+
+### Temporary extension
+
+- `type`: `temp`
+
+### Callgroup extension
+
+- `type`: `callgroup`
+- `callgroup_members`: List of extension numbers that belong to this callgroup.
diff --git a/mkdocs.yml b/mkdocs.yml
index 9129dc0..a41b836 100644
--- a/mkdocs.yml
+++ b/mkdocs.yml
@@ -16,3 +16,5 @@ nav:
   - Reference:
     - reference/command-line-options.md
     - reference/configuration.md
+    - reference/extensions.md
+    - reference/controller.md