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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent, closed-world mutation. The description adds one piece of value beyond that: the Pro-plan prerequisite. It says nothing about duplicate/conflict behavior, which matters given idempotentHint=false and the existence of update_goal.

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?

Two short sentences with zero filler and the core action front-loaded. It is efficient, though so terse that the second sentence carries the entire differentiation and prerequisite load.

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?

An output schema and annotations cover the return shape and safety profile, so those needn't be described. But for a 5-parameter creation tool where activityId/activityName are both optional yet one is evidently needed, and where a duplicate goal would presumably collide with update_goal, the description leaves real gaps.

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 80%, so the schema already explains goalType, activityId, activityName, and targetMinutes. The description's 'weekly or monthly' merely restates the period enum and adds no syntax 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 ('Set') and resource ('a weekly or monthly time goal for an activity'), which is clearly distinct from get_goal_progress and delete_goal. It does not, however, differentiate itself from the sibling update_goal, leaving the create-vs-modify boundary implicit.

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 only guidance is the embedded prerequisite 'Pro feature', which is genuinely useful context. There is no statement of when to use create_goal versus update_goal, nor what to do if a goal for the activity already exists, so usage is only implied.

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