selection_add

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

With no annotations present, the description carries the burden, and it does disclose the key behavioral trait: the operation is additive and preserves the existing selection. It does not cover error behavior or invalid-target handling, but those are secondary for a simple selection mutation.

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?

A single, front-loaded sentence conveys the action and the critical caveat with no wasted words. It is immediately scannable and 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?

For a one-parameter mutation with no output schema, the description plus schema is nearly complete. The main missing context is explicit guidance on alternate selection tools and error behavior, but an agent can safely invoke this tool based on what is provided.

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?

The schema covers 100% of the parameters, so the description is not required to compensate. It adds no new meaning beyond the schema's definition of targets as Instance paths or UUIDs, which is sufficient.

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 ('Add'), a precise resource ('Instances to the current Roblox Studio selection'), and the distinguishing behavior ('without deselecting currently selected objects'). This clearly differentiates it from sibling selection_set and selection_clear.

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 phrase 'without deselecting currently selected objects' implies an additive use case, so an agent can infer when to choose it over selection_set. However, the description does not explicitly name alternatives or state when not to use this tool.

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