app_usage

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful context about how the data is computed ('from summed segment durations') and states the limit bounds. However, it does not disclose return format, pagination, or behavior when no data exists, so it does not go far beyond annotations.

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?

The description is compact, front-loaded with the core purpose, and includes a clearly formatted Args block. Every sentence contributes necessary information without redundancy or fluff.

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?

Given the tool's simplicity, the presence of an output schema, and strong annotations, the description covers the essential inputs and purpose. It does not explain when to use it vs siblings, but for a straightforward query tool that may be acceptable. The description is sufficiently complete for an agent to invoke it correctly.

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 0%, so the description bears the full burden of explaining parameters. It does this well: start and end are defined as 'ISO 8601 local start/end of the window', and limit is specified as '1-100, default 20'. The only minor issue is that the schema lists limit's default as null while the description says 20, a slight inconsistency in default value specification.

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 clearly states the tool reports 'Time spent per app over a window', specifying both the resource (apps) and the scope (time window). It does not explicitly use a verb like 'get' or 'list', but the intent is unambiguous. It does not differentiate from sibling tools, but its focus on app usage is distinct enough.

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 provides no guidance on when to use this tool versus alternatives. It does not mention any context or exclusions, such as 'use this for aggregated usage, use list_segments for raw segments'. The only implied context is a time window, but no explicit usage scenario is described.

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