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

Annotations already declare the full behavioral profile (not read-only, idempotent, non-destructive, closed-world), and the description adds nothing beyond the "(tag)" synonym. It does not say what happens when the label already exists (covered only implicitly by idempotentHint) or whether the activity must be owned by the caller.

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 short sentence with the verb and resource front-loaded and zero filler. Nothing could be removed without losing 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 two-parameter, 100%-documented, non-destructive tool with complete annotations, the description covers the essentials. It is slightly thin in that no output schema exists and the description says nothing about the result of adding a label or duplicate handling, but this is minor for such a simple operation.

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 both parameters (label, activity_id) are already fully documented in the schema, including the 127-character limit. The description adds only the parenthetical synonym and no format or constraint detail 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 ("Add") and resource ("label") and clarifies the synonym "tag", so the agent knows exactly what the tool does. It does not, however, differentiate itself from the sibling remove_label or from update_activity, which also touch activity metadata.

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?

There is no when-to-use or when-not-to-use guidance. With remove_label sitting in the sibling list, the description could have stated that this adds rather than removes a label, but it leaves that inference entirely to the tool name.

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