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

No annotations exist, so the description carries the burden and does reasonably well: it discloses the default-year behavior, the historical data floor of FY2022, the two rate schedules, and what the payload contains. It does not cover failure modes (e.g., an unknown SIN) or the role of the verification_url flag, which is left to the schema.

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?

Front-loaded with the core purpose, then defaults, then data availability — a sensible information order. The opening phrase duplicates the tool name and the second sentence repeats 'GSA Fleet vehicle leasing rates', a small amount of waste but nothing obstructive.

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?

With no output schema, the description correctly states the returned values (monthly lease rate and rate per mile), and it scopes the data by schedule and fiscal year. The one gap is behavior for invalid or unsupported SIN/year combinations, but for a simple read-only lookup this is close to complete.

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 75%, and the description adds meaning the schema lacks: what happens when 'year' is omitted and the earliest year that will resolve. It also characterizes the unit of 'sin' (a vehicle type) and the standard/europe split, though the latter is largely restated from the schema's enum description.

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?

Specific verb and resource: 'Return the GSA Fleet vehicle leasing rates (monthly lease rate and rate per mile) for the vehicle type identified by its Standard Item Number (SIN)'. Names the scope (standard vs europe rate schedule) and even the returned metrics, so no sibling tool could be mistaken for it.

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?

Gives the key selection condition ('If year is not specified, the current fiscal year's rates will be returned') and the availability window ('Rates are available from fiscal year 2022'), which tells the agent when a year lookup is valid. No explicit exclusion of alternatives, but no sibling covers fleet leasing rates, so routing ambiguity is minimal.

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