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

Annotations only declare read-only/non-destructive/open-world. The description adds substantial behavioral context beyond that: available is false until a month is explained, pending_aircraft are excluded from level and change, change.restated is reported beside the move rather than inside it, and amounts are nominal dollars.

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 purpose and the sibling alternative are front-loaded in the first and last sentences, and every clause is dense with domain meaning. However, a large middle block explains output field relationships (change.amount, level.typical, level.fleet) that an output schema already carries, making it longer than strictly necessary.

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 complex domain tool the description covers the caveats an agent needs (pending exclusion, availability gating, restated handling, nominal dollars) and the annotations carry the safety profile. It leans heavily on restating output structure that the output schema already defines, so it is complete but not optimally partitioned.

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?

There is a single parameter, portfolio_id, and schema description coverage is 100% ('From list_portfolios.'). The description adds no syntax, format, or sourcing detail beyond the schema, so the baseline 3 for high-coverage schemas 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?

The first sentence states a specific verb+resource+scope: one portfolio's value by driver at every month start of its history, oldest first. It explicitly distinguishes itself from the sibling get_portfolio_attribution ('for the last day, week or month with the aircraft behind it'), so an agent can route correctly without opening either schema.

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?

Names the alternative tool and the exact condition that selects it (recent day/week/month snapshots vs. full monthly history). It also gives an operational rule for the pending_aircraft edge case: report the breakdown as being updated rather than quoting it when pending share is large.

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