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

With no annotations, the description carries the full burden and does well: it discloses provenance (model checked to the cent against an independent calculator), that card terms were human-verified against issuer pages, and that the response reports catalog version and last-checked dates. It also discloses a side effect (apply clicks attributed to the source slug) via the required source parameter. It does not state rate limits or confirm the operation is read-only/no destructive side effects.

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?

Four sentences, front-loaded with what is returned, followed by provenance and the two display obligations. Every sentence carries information; only the sourcing sentence is somewhat dense but it justifies itself by establishing trust in the numbers.

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 9 parameters, nested objects and no output schema, the description does the heavy lifting by enumerating the return contents: top three cards, best two-card combo, post-fee value over the horizon, catalog version, last-checked dates, continueUrl and disclosure. That is enough for an agent to know what comes back, though exact field shapes remain unspecified.

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%, so the schema already documents every parameter, including the totals category constraint and the years enum. The description adds little parameter-level detail beyond 'a year of spending by category' and 'the chosen horizon', 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 description gives a specific verb and resource: given a year of spending by category, it returns the three best cards plus the best two-card combination valued after annual fee. That is concrete and unambiguous. It does not, however, distinguish itself from siblings compare_two or keep_or_cancel, which an agent would need to route correctly.

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 names a prerequisite workflow by pointing to the spending_categories tool to map the statement onto categories first, and it prescribes two mandatory follow-up actions (show continueUrl, show disclosure string). What is missing is any explicit guidance on when to prefer compare_two or keep_or_cancel instead of this simulation.

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