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

Annotations already cover the safety profile (readOnly, non-destructive, closed world), and the description still adds substantial behavioral context: future dates honor logged journeys then continue presence in the last destination, open journey gaps block the calculation, and the result includes uncertain/unowned days plus the countingMethod per country. The "informational, not tax advice" caveat is exactly the kind of non-obvious framing an agent needs before relaying output.

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?

Six short, front-loaded sentences that each carry real information, with the core computation stated first and caveats after. The one redundancy is the enumeration of returned fields ("status, presence blocks, unowned uncertain days, countingMethod"), which duplicates the output schema and could be trimmed.

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 two-parameter, zero-required, read-only calculation tool with an output schema and full annotation coverage, the description supplies everything an agent needs: the computation, the default date behavior, future-date semantics, the blocking condition (open journey gaps), and a fallback guide tool for unfamiliar callers.

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 100% and both parameters already carry their own semantics, including the future-date and open-journey-gap behavior for asOf. The description restates the asOf default ("Omit asOf for today") and adds nothing about personId's omission default beyond what the schema says, 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?

The first sentence names a concrete computation (days of presence per country vs. that country's residency threshold and window), which is far more specific than a restated title. It implicitly separates itself from check_schengen_status by tying the result to tax-residency thresholds rather than a Schengen day limit, but it never names that sibling, so the differentiation is left to inference.

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 gives a clear default rule ("Omit asOf for today") and an explicit prerequisite path ("If unfamiliar with TripLedger semantics, call get_tripledger_guide first"). What it lacks is any statement of when NOT to use this tool or an explicit pointer to check_schengen_status when the user actually wants Schengen days rather than tax residency.

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