set_mid_scalar_param

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

Adds real context beyond the annotations: the MID is transient, the change is immediate, never saved, and an invalid name is refused with nothing written. This helps the agent understand the non-persistent mutation semantics and failure mode that readOnlyHint/destructiveHint/idempotentHint alone don't convey.

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 action, scope, and alternative routing are front-loaded in the first sentence, with constraints and the Returns block after. It is dense with semicolons but every clause carries information; only slight trimming is possible.

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?

With 3 fully-required params, no output schema, and complete annotations, the description covers the mutation semantics, the precondition, the failure behavior, and even the return fields. Complete enough to call correctly; only cross-tool scalar alternatives and cross-type disambiguation are lightly handled.

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 already 100%, so the baseline is 3, but the description adds provenance for mid_object_path (returned by create_material_instance_dynamic / create_dynamic_material_on_actor) and tightens param_name to a global scalar parameter. This is meaningfully more than the schema text provides.

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?

States a specific verb and resource ('Set a scalar parameter override on a transient MID') and immediately names the sibling tools for the other data types (set_mid_vector_param, set_mid_texture_param). An agent can distinguish it from every nearby set_mid_*/set_material_instance_param tool without opening a 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?

Gives clear routing guidance for the vector/texture cases and a hard precondition ('param_name must be a global scalar parameter... as get_mid_all_params lists it'). It does not explicitly contrast against other scalar-setting tools like set_material_instance_param or set_mpci_scalar_parameter_value, so the when-not is only partially covered.

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