set_parameterUpdate a user parameter's value in Fusion 360 by providing its name and a new numeric value.
Update the value of an existing user parameter
| Name | Required | Description | Default |
|---|---|---|---|
| name | Yes | Parameter name | |
| value | Yes | New numeric value, expressed in the unit the parameter already declares |
Changes observed during successful MCP inspections.
v0.1.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=false, idempotentHint=true, and destructiveHint=false, so the mutation is safely characterized. The description adds the 'existing' constraint but does not disclose failure behavior, side effects, or what happens when the parameter does not exist.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, front-loaded sentence with no filler. It communicates the action and object directly, earning its place with zero waste.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple two-parameter, idempotent update with full schema coverage and no output schema, the description is nearly sufficient. It could have explicitly noted how missing parameters are handled, but the 'existing' wording covers the main prerequisite.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% with clear descriptions for both `name` and `value`, including the unit semantics for `value`. The description adds only the broader 'existing' context, not meaningful per-parameter detail beyond the schema.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description states a specific verb ('Update'), a clear resource ('the value of an existing user parameter'), and the scope ('existing'), which distinguishes it from siblings like create_parameter, delete_parameter, and get_parameters. An agent can tell what this tool does without opening the schema.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The word 'existing' implies this is not for creating new parameters, and sibling names suggest alternatives, but the description never explicitly says when to use this tool versus create_parameter or get_parameters. Usage context is implied rather than stated.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.