diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7c57b5b..330b9d7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -161,4 +161,9 @@ install(DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/ui/dist/"
 	OPTIONAL
 )
 
+install(DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/docs/"
+	DESTINATION "docs"
+	OPTIONAL
+)
+
 source_group(TREE "${APP_DIR}" FILES ${APP_SOURCES})
diff --git a/docs/openapi.yaml b/docs/openapi.yaml
new file mode 100644
index 0000000..dc8db5f
--- /dev/null
+++ b/docs/openapi.yaml
@@ -0,0 +1,503 @@
+openapi: 3.0.3
+info:
+  title: Video Shader Toys Control API
+  version: 0.1.0
+  description: |
+    REST API exposed by the local Video Shader Toys control server.
+
+    The API is intended for local control tools and the bundled React UI. All mutating
+    endpoints return a small action result object. Successful mutating requests also
+    broadcast the latest runtime state over the `/ws` WebSocket.
+
+    WebSocket state streaming is not described by OpenAPI; connect to `ws://127.0.0.1:{port}/ws`
+    to receive full runtime state JSON messages whenever state changes.
+servers:
+  - url: http://127.0.0.1:8080
+    description: Default local control server
+tags:
+  - name: State
+    description: Runtime state and status.
+  - name: Layers
+    description: Layer stack control.
+  - name: Stack Presets
+    description: Save and recall layer stack presets.
+  - name: Runtime
+    description: Runtime actions.
+paths:
+  /api/state:
+    get:
+      tags: [State]
+      summary: Get current runtime state
+      operationId: getRuntimeState
+      responses:
+        "200":
+          description: Current runtime state.
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/RuntimeState"
+  /api/layers/add:
+    post:
+      tags: [Layers]
+      summary: Add a layer using a shader package
+      operationId: addLayer
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/AddLayerRequest"
+      responses:
+        "200":
+          $ref: "#/components/responses/ActionOk"
+        "400":
+          $ref: "#/components/responses/ActionError"
+  /api/layers/remove:
+    post:
+      tags: [Layers]
+      summary: Remove a layer
+      operationId: removeLayer
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/LayerIdRequest"
+      responses:
+        "200":
+          $ref: "#/components/responses/ActionOk"
+        "400":
+          $ref: "#/components/responses/ActionError"
+  /api/layers/move:
+    post:
+      tags: [Layers]
+      summary: Move a layer by direction
+      description: Moves a layer up or down by one or more positions, depending on the signed direction value.
+      operationId: moveLayer
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/MoveLayerRequest"
+      responses:
+        "200":
+          $ref: "#/components/responses/ActionOk"
+        "400":
+          $ref: "#/components/responses/ActionError"
+  /api/layers/reorder:
+    post:
+      tags: [Layers]
+      summary: Move a layer to an absolute index
+      operationId: reorderLayer
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/ReorderLayerRequest"
+      responses:
+        "200":
+          $ref: "#/components/responses/ActionOk"
+        "400":
+          $ref: "#/components/responses/ActionError"
+  /api/layers/set-bypass:
+    post:
+      tags: [Layers]
+      summary: Set layer bypass state
+      operationId: setLayerBypass
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/SetBypassRequest"
+      responses:
+        "200":
+          $ref: "#/components/responses/ActionOk"
+        "400":
+          $ref: "#/components/responses/ActionError"
+  /api/layers/set-shader:
+    post:
+      tags: [Layers]
+      summary: Change the shader package used by a layer
+      operationId: setLayerShader
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/SetShaderRequest"
+      responses:
+        "200":
+          $ref: "#/components/responses/ActionOk"
+        "400":
+          $ref: "#/components/responses/ActionError"
+  /api/layers/update-parameter:
+    post:
+      tags: [Layers]
+      summary: Update a layer parameter value
+      operationId: updateLayerParameter
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/UpdateParameterRequest"
+      responses:
+        "200":
+          $ref: "#/components/responses/ActionOk"
+        "400":
+          $ref: "#/components/responses/ActionError"
+  /api/layers/reset-parameters:
+    post:
+      tags: [Layers]
+      summary: Reset a layer's parameters to shader defaults
+      operationId: resetLayerParameters
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/LayerIdRequest"
+      responses:
+        "200":
+          $ref: "#/components/responses/ActionOk"
+        "400":
+          $ref: "#/components/responses/ActionError"
+  /api/stack-presets/save:
+    post:
+      tags: [Stack Presets]
+      summary: Save the current layer stack as a preset
+      operationId: saveStackPreset
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/PresetNameRequest"
+      responses:
+        "200":
+          $ref: "#/components/responses/ActionOk"
+        "400":
+          $ref: "#/components/responses/ActionError"
+  /api/stack-presets/load:
+    post:
+      tags: [Stack Presets]
+      summary: Load a layer stack preset
+      operationId: loadStackPreset
+      requestBody:
+        required: true
+        content:
+          application/json:
+            schema:
+              $ref: "#/components/schemas/PresetNameRequest"
+      responses:
+        "200":
+          $ref: "#/components/responses/ActionOk"
+        "400":
+          $ref: "#/components/responses/ActionError"
+  /api/reload:
+    post:
+      tags: [Runtime]
+      summary: Reload shaders
+      operationId: reloadShaders
+      requestBody:
+        required: false
+        content:
+          application/json:
+            schema:
+              type: object
+              additionalProperties: false
+      responses:
+        "200":
+          $ref: "#/components/responses/ActionOk"
+        "400":
+          $ref: "#/components/responses/ActionError"
+components:
+  responses:
+    ActionOk:
+      description: Action succeeded.
+      content:
+        application/json:
+          schema:
+            $ref: "#/components/schemas/ActionResponse"
+          example:
+            ok: true
+    ActionError:
+      description: Action failed or request JSON was invalid.
+      content:
+        application/json:
+          schema:
+            $ref: "#/components/schemas/ActionResponse"
+          example:
+            ok: false
+            error: Unknown layer id.
+  schemas:
+    ActionResponse:
+      type: object
+      required: [ok]
+      properties:
+        ok:
+          type: boolean
+        error:
+          type: string
+          description: Present when the request fails or when the runtime returns a diagnostic.
+      additionalProperties: false
+    AddLayerRequest:
+      type: object
+      required: [shaderId]
+      properties:
+        shaderId:
+          type: string
+          example: studio-color
+      additionalProperties: false
+    LayerIdRequest:
+      type: object
+      required: [layerId]
+      properties:
+        layerId:
+          type: string
+          example: layer-1
+      additionalProperties: false
+    MoveLayerRequest:
+      type: object
+      required: [layerId, direction]
+      properties:
+        layerId:
+          type: string
+        direction:
+          type: integer
+          description: Signed movement direction. Negative moves toward the top of the stack; positive moves toward the bottom.
+          example: -1
+      additionalProperties: false
+    ReorderLayerRequest:
+      type: object
+      required: [layerId, targetIndex]
+      properties:
+        layerId:
+          type: string
+        targetIndex:
+          type: integer
+          minimum: 0
+          example: 0
+      additionalProperties: false
+    SetBypassRequest:
+      type: object
+      required: [layerId, bypass]
+      properties:
+        layerId:
+          type: string
+        bypass:
+          type: boolean
+      additionalProperties: false
+    SetShaderRequest:
+      type: object
+      required: [layerId, shaderId]
+      properties:
+        layerId:
+          type: string
+        shaderId:
+          type: string
+          example: vhs
+      additionalProperties: false
+    UpdateParameterRequest:
+      type: object
+      required: [layerId, parameterId, value]
+      properties:
+        layerId:
+          type: string
+        parameterId:
+          type: string
+          example: brightness
+        value:
+          description: Parameter value. Type depends on the shader parameter definition.
+          oneOf:
+            - type: number
+            - type: boolean
+            - type: string
+            - type: array
+              items:
+                type: number
+          example: 1.25
+      additionalProperties: false
+    PresetNameRequest:
+      type: object
+      required: [presetName]
+      properties:
+        presetName:
+          type: string
+          example: live-show-look
+      additionalProperties: false
+    RuntimeState:
+      type: object
+      properties:
+        app:
+          $ref: "#/components/schemas/AppState"
+        runtime:
+          $ref: "#/components/schemas/RuntimeStatus"
+        video:
+          $ref: "#/components/schemas/VideoStatus"
+        decklink:
+          $ref: "#/components/schemas/DeckLinkStatus"
+        performance:
+          $ref: "#/components/schemas/PerformanceStatus"
+        shaders:
+          type: array
+          items:
+            $ref: "#/components/schemas/ShaderSummary"
+        stackPresets:
+          type: array
+          items:
+            type: string
+        layers:
+          type: array
+          items:
+            $ref: "#/components/schemas/LayerState"
+    AppState:
+      type: object
+      properties:
+        serverPort:
+          type: number
+        autoReload:
+          type: boolean
+        maxTemporalHistoryFrames:
+          type: number
+        enableExternalKeying:
+          type: boolean
+        videoFormat:
+          type: string
+        frameRate:
+          type: string
+    RuntimeStatus:
+      type: object
+      properties:
+        layerCount:
+          type: number
+        compileSucceeded:
+          type: boolean
+        compileMessage:
+          type: string
+    VideoStatus:
+      type: object
+      properties:
+        hasSignal:
+          type: boolean
+        width:
+          type: number
+        height:
+          type: number
+        modeName:
+          type: string
+    DeckLinkStatus:
+      type: object
+      properties:
+        modelName:
+          type: string
+        supportsInternalKeying:
+          type: boolean
+        supportsExternalKeying:
+          type: boolean
+        keyerInterfaceAvailable:
+          type: boolean
+        externalKeyingRequested:
+          type: boolean
+        externalKeyingActive:
+          type: boolean
+        statusMessage:
+          type: string
+    PerformanceStatus:
+      type: object
+      properties:
+        frameBudgetMs:
+          type: number
+        renderMs:
+          type: number
+        smoothedRenderMs:
+          type: number
+        budgetUsedPercent:
+          type: number
+    ShaderSummary:
+      type: object
+      properties:
+        id:
+          type: string
+        name:
+          type: string
+        description:
+          type: string
+        category:
+          type: string
+        temporal:
+          $ref: "#/components/schemas/TemporalState"
+    TemporalState:
+      type: object
+      properties:
+        enabled:
+          type: boolean
+        historySource:
+          type: string
+          enum: [source, preLayerInput, none]
+        requestedHistoryLength:
+          type: number
+        effectiveHistoryLength:
+          type: number
+    LayerState:
+      type: object
+      properties:
+        id:
+          type: string
+        shaderId:
+          type: string
+        shaderName:
+          type: string
+        bypass:
+          type: boolean
+        temporal:
+          $ref: "#/components/schemas/TemporalState"
+        parameters:
+          type: array
+          items:
+            $ref: "#/components/schemas/ParameterState"
+    ParameterState:
+      type: object
+      properties:
+        id:
+          type: string
+        label:
+          type: string
+        type:
+          type: string
+          enum: [float, vec2, color, bool, enum]
+        min:
+          type: array
+          items:
+            type: number
+        max:
+          type: array
+          items:
+            type: number
+        step:
+          type: array
+          items:
+            type: number
+        options:
+          type: array
+          items:
+            $ref: "#/components/schemas/ParameterOption"
+        value:
+          description: Current parameter value.
+          oneOf:
+            - type: number
+            - type: boolean
+            - type: string
+            - type: array
+              items:
+                type: number
+    ParameterOption:
+      type: object
+      properties:
+        value:
+          type: string
+        label:
+          type: string