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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower, and the description still adds real context: it discloses the data sources ('from the ledger or the filed accounts'), the segmentation of results (completed years, current YTD against same months last year, plus a trend interpretation), and a precondition (company must have history). That is substantive beyond the 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 purpose and the usage trigger are front-loaded, which is good, but the middle of the description degenerates into a keyword list ('revenue and profit trend, margin, cash at year end, year on year, same time last year, how did last year go') that partially duplicates itself across two clauses. Roughly a third of the text could be cut without losing information.

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 carries the burden of describing results, and it does so reasonably: completed years, YTD comparison, and a qualitative trend read. It omits anything about response shape, units, currency handling, or how many years are returned, which prevents a 5 for a read tool with no output schema.

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 optional parameter with 100% schema description coverage, so the schema already explains company name/id and the list_companies reference. The description adds nothing about the parameter and instead repeats the concept of 'same time last year' as free text, so 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 opening clause names the resource (year-on-year comparison) and enumerates the concrete measures returned (revenue and profit trend, margin, cash at year end). It is distinguishable from siblings like get_profit_and_loss or get_balance_sheet, though it never names a sibling to route away from, which keeps it at 4 rather than 5.

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 an explicit trigger: use before any 'how are we doing', planning or forecasting answer when the company has history. That is clear situational guidance, but there are no explicit exclusions (e.g., what to use instead for a single-period view or when there is no history), so it falls short of 5.

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