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material_instance_set_params

Update an existing material instance by setting scalar, vector, or texture parameter overrides, then save the changes.

Instructions

Set scalar/vector/texture parameters on an existing material instance, then save.

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": {
      "material_instance": "<material_instance>"
    },
    "name": "material_instance_set_params"
  }
}

Input Schema

NameRequiredDescriptionDefault
scalar_paramsNoScalar parameter overrides: {ParamName: value}.
vector_paramsNoVector parameter overrides: {ParamName: [r, g, b, a?]}.
texture_paramsNoTexture parameter overrides: {ParamName: texture asset path}.
material_instanceYesMaterialInstanceConstant asset path.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.4.0

TDQS

A3.9/5.0
Behavior3/5

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

No annotations are provided, so the description carries the burden of disclosing behavior. It states the mutating nature ('set') and the persistence ('then save'), but does not explain whether parameters are overwritten entirely, what happens if a parameter name is invalid, or any side effects on the asset's saved state.

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

Conciseness5/5

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

One sentence, front-loaded with a specific verb and resource, and no filler. It efficiently conveys the core operation and the save step.

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

Completeness3/5

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

With no output schema and no annotations, the description is relatively thin for a tool involving 4 parameters and nested objects. It conveys the essential action but omits details like error behavior, whether all parameters must be overridden or only provided ones, and what the saved outcome looks like. Still, it is adequate for straightforward invocations.

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

Parameters3/5

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

The schema provides 100% coverage with descriptive text for each parameter, including types and structure. The description groups parameters into scalar/vector/texture, which adds minimal additional meaning beyond the schema's own documentation.

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

Purpose5/5

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

The description clearly states the specific action ('Set scalar/vector/texture parameters') and the resource ('existing material instance'), distinguishing it from sibling tools like material_instance_create (creation) and material_apply (applying a material). The inclusion of 'then save' adds a clear end-to-end behavior.

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

Usage Guidelines4/5

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

The description specifies the context: modifying parameters on an existing material instance. This implies it is not for creating new instances or applying materials, which are covered by sibling tools. However, it does not explicitly name alternatives or state when NOT to use it.

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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