activity_timeline

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

With no annotations, the description carries the full burden and does so well. It discloses local-hour/midnight alignment, accepted time formats, defaults, and the truncation behavior signaled by `truncated: true`. These are behavioral details an agent could not infer from the schema alone.

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 dense but well-organized, front-loading the output shape and purpose before moving to parameters and edge cases. Every clause adds useful information with no filler.

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 moderately complex query tool, the description covers output fields, timezone alignment, input formats, defaults, and truncation behavior. Combined with the existing output schema, an agent has everything needed to select and invoke this tool 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%, but the description fully compensates by explaining all three parameters: `bucket` options and alignment, `since`/`until` accepted formats and defaults, and the meaning of omitting `until`. Each parameter gets more meaning than its bare schema representation provides.

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 defines the tool's resource as 'the user's activity over time' and its purpose as showing 'when work happened rather than how much.' This distinguishes it from sibling tools like prompt_stats and time_summary even without naming them.

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?

It explicitly guides when to use the tool: to show the shape of activity rather than volume. It also gives actionable advice on handling wide windows by widening the bucket instead of the window. It doesn't name sibling alternatives explicitly, but the when/not distinction is clear enough.

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