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diff --git a/doc/api/README.md b/doc/api/README.md
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--- a/doc/api/README.md
+++ b/doc/api/README.md
@@ -23,6 +23,7 @@
 - [Namespaces](namespaces.md)
 - [Settings](settings.md)
 - [Keys](keys.md)
+- [Variables](variables.md)
 
 ## Clients
 
diff --git a/doc/api/variables.md b/doc/api/variables.md
new file mode 100644
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+++ b/doc/api/variables.md
@@ -0,0 +1,106 @@
+# Variables
+
+## Variables keys
+
+All variable keys must contains only letters, digits and '\_'. They must also be no longer than 255 characters.
+
+## List project variables
+
+Get list of variables of a project.
+
+```
+GET /projects/:id/variables
+```
+
+Parameters:
+
+- `id` (required) - The ID of a project
+
+```json
+[
+    {
+        "key": "TEST_VARIABLE_1",
+        "value": "TEST_1"
+    },
+    {
+        "key": "TEST_VARIABLE_2",
+        "value": "TEST_2"
+    }
+]
+```
+
+## Show variable details
+
+Get details of specifica variable of a project.
+
+```
+GET /projects/:id/variables/:key
+```
+
+Parameters:
+
+- `id` (required) - The ID of a project
+- `key` (required) - The `key` of variable
+
+```json
+{
+    "key": "TEST_VARIABLE_1",
+    "value": "TEST_1"
+}
+```
+
+## Create variable
+
+Create new variable in project.
+
+```
+POST /projects/:id/variables
+```
+
+Parameters:
+
+- `id` (required) - The ID of a project
+- `key` (required) - The `key` for variable
+- `value` (required) - The `value` for variable
+
+```json
+{
+    "key": "NEW_VARIABLE",
+    "value": "new value"
+}
+```
+
+## Update variable
+
+Update variable.
+
+```
+PUT /projects/:id/variables/:key
+```
+
+Parameters:
+
+- `id` (required) - The ID of a project
+- `key` (required) - The `key` for variable
+- `value` (required) - The `value` for variable
+
+```json
+{
+    "key": "NEW_VARIABLE",
+    "value": "updated value"
+}
+```
+
+## Remove variable
+
+Remove variable.
+
+```
+DELETE /projects/:id/variables/:key
+```
+
+Parameters:
+
+- `id` (required) - The ID of a project
+- `key` (required) - The `key` for variable
+