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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the safety profile is covered. The description adds useful behavioral detail beyond annotations: it shows what event types are included (upgrades, downgrades, outlook changes) and warns about limited company coverage. It does not mention pagination or empty results, but that is partly covered by the output schema and parameter descriptions.

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?

Two tightly written sentences. The first sentence states the purpose, and the second adds content detail and a valuable coverage caveat without wasted words or repetition of schema fields.

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 read-only look-up tool with one required parameter, a fully described schema, and an output schema, the description is complete. It explains the domain, the included data types, and the sparse coverage for NZX companies. Nothing an agent needs in order to decide whether and how to call this tool is missing.

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%, with every parameter already documented. The description does not add substantial parameter-specific meaning beyond the schema; it merely reinforces the domain context. A baseline of 3 is appropriate because the schema carries the parameter documentation burden.

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 opens with a specific verb and resource ('Get credit rating history for an NZX company') and immediately clarifies the subject matter by naming the agencies and event types. This clearly distinguishes it from other NZX company tools like get_financials or get_stock_prices, even without an explicit sibling comparison.

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?

The description states clear context: this is for NZX company credit rating history, covering four named agencies. The caveat that only ~20 NZX companies have credit ratings helps the agent set expectations and avoid calling it for tickers likely to have no data. It does not name alternatives, but no direct alternative exists among the siblings, so the context is sufficient.

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