add_geometry_collection_source

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

Goes well beyond the annotations (readOnlyHint=false, idempotentHint=false, destructiveHint=false) by disclosing that the change is only persisted when the package reaches disk and that a failed save leaves the mutation in memory only, with saved=false and a save_error. This is exactly the kind of failure-mode context annotations cannot 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?

Front-loaded with the core action in the first clause, followed by the save semantics. The explicit Returns block is justified because there is no output schema. Slightly list-like but every part earns its place.

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 no output schema, the description compensates by enumerating the return fields (num_sources, num_materials, success, saved, save_error). Combined with the save/persistence semantics, an agent has everything needed to call it correctly and interpret the result.

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 description coverage is 100%, so the schema already documents geometry_collection_path, source_mesh_path, and the optional transform. The description adds no parameter-level meaning beyond the schema, so the baseline 3 applies.

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 (append) and resource (an additional StaticMesh source to an existing geometry collection), plus the save side effect. This clearly distinguishes it from siblings like create_geometry_collection and remove_geometry_collection_source without needing to open any 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' signals the prerequisite that the collection must already exist, and 'then save it' clarifies the post-condition. It gives clear context for when to call it but does not explicitly name alternatives (e.g. create vs remove source) 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.