Create User Coordinate System

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

Annotations cover the safety profile (readOnly=false, idempotent=false, destructive=false), but the description adds a genuinely non-obvious side effect: a hidden anchor sketch is created and must not be deleted. That is behavior an agent could not infer from the schema or annotations. It stops short of covering naming conflicts or failure behavior.

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?

Three sentences, front-loaded with what is created, then the side effect, then the unit convention. No filler and each sentence carries a distinct piece of information.

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 7-parameter, all-optional tool with no output schema and no annotations beyond hints, the description covers purpose, units, preview status and the hidden-sketch caveat. It is slightly thin on the active-design/component context the UCS is created in and does not mention any return value, though nothing critical is missing.

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% and each parameter already carries a unit annotation, so the baseline is 3. The description earns above baseline by reinforcing the cross-cutting unit convention ('cm, not mm') and noting that per-parameter overrides exist, which guards against the common mm assumption in Fusion workflows.

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 ('Create a UCS') plus the key coordinate inputs and optional rotation. No sibling tool creates a UCS, so there is nothing to confuse it with, and the parenthetical version note adds precision.

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 description flags that this relies on the Fusion 2026+ UCS API and is in preview, which is real usage context, but it never states when to reach for this versus, say, create_construction_plane or create_construction_axis, nor any prerequisites.

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