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

Annotations already declare the full safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false, openWorldHint=false), so the description's job is lighter. It adds no behavioral context of its own though, such as whether duplicate names are allowed, what happens to existing activities, or whether the new activity starts active. That gap is tolerable given annotations plus an output schema, but nothing extra is contributed.

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 with no wasted words. It is efficient, though for a mutation tool with four parameters it is arguably undersized rather than optimally sized.

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 exists, so return values need not be explained, and annotations cover the safety profile. However, for a create operation the description says nothing about name uniqueness, whether the activity is immediately active, or what the created-at state is, leaving an agent to infer behavior from the schema alone.

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 50%: color and timeSpendingPreference already carry their own descriptions and the enum is restricted, while name (required, 1-50 chars) and description (<=200 chars) are self-evident from their types. The description adds no parameter meaning, so the schema is doing all the work, which lands at the baseline.

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 gives a specific verb and resource ("Create a new activity") plus a purpose clause ("to track time against"), which separates it from create_goal and the timer/logging siblings. It stops short of explicitly naming siblings, but the resource is unambiguous.

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 "to track time against" implies the workflow (create an activity before logging time to it), but there is no explicit when-to-use versus update_activity/archive_activity guidance and no prerequisites or exclusions stated.

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