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OBS MCP

OBS MCP

by Tom-R-Main
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Rust
Hybrid

Set Scene Item Blend Mode

obs-set-scene-item-blend-mode
Idempotent

Set a scene item's blend mode to control how it composites with layers below. Choose from normal, additive, subtract, screen, multiply, lighten, or darken.

Instructions

Set the blend mode of a scene item

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "sceneItemId": "<sceneItemId>",
      "sceneItemBlendMode": "<sceneItemBlendMode>"
    },
    "name": "obs-set-scene-item-blend-mode"
  }
}

Input Schema

NameRequiredDescriptionDefault
sceneNameNoName of the scene
sceneUuidNoUUID of the scene
canvasUuidNoUUID of the canvas containing the scene
sceneItemIdYesNumeric ID of the scene item
sceneItemBlendModeYes

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.1.1

TDQS

C2.4/5.0
Behavior3/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already declare readOnlyHint=false and idempotentHint=true, so the agent knows this is a state-changing but idempotent operation. The description adds nothing beyond the annotations; no mention of what happens to existing blend modes or if the operation is permanent, but since annotations cover the basic safety profile, this is acceptable.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness2/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is ultra-brief (one sentence) but fails to include essential usage context or parameter semantics. It is under-specified rather than concise; the description should have leveraged its brevity to add key guidance.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness2/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With 5 parameters (including sceneName, sceneUuid, canvasUuid) and no output schema, the description leaves the agent without guidance on which identification method is preferred, the impact of multiple scene identifiers, or the effect of invalid IDs. The description is not complete enough for a tool with this complexity.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The schema itself has high coverage (80%) for most parameters, but the sceneItemBlendMode enum values (e.g., OBS_BLEND_NORMAL) are not explained in the schema or description, leaving the agent without semantic guidance on which blend mode does what. The description does not compensate for this gap; thus, the score is below baseline.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose3/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description 'Set the blend mode of a scene item' is clear but spans only one line and does not differentiate from sibling tools like obs-get-scene-item-blend-mode or obs-set-scene-item-enabled. It is not a tautology, but it lacks specifics about the effect or scope.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description provides no guidance on when to use this tool versus alternatives, nor does it mention prerequisites such as the need to first retrieve the scene item ID. No context is provided for selecting a scene by name vs UUID.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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