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

The annotations already communicate that the tool is read-only, idempotent, and non-destructive. The description adds meaningful behavioral context by explaining the two different response shapes: a concept catalog versus a time series of values. This goes beyond the annotations without contradicting them.

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 description is two well-structured sentences with no filler. The primary purpose is stated first, followed by a concise explanation of the two usage modes. Every sentence contributes useful 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?

Given that there is no output schema, the description does a good job of explaining the return behavior at a high level. It covers the catalog mode and the time-series mode, and the schema fully documents all parameters. A little more detail about the exact output structure would improve completeness, but it is not necessary for correct invocation.

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?

The input schema already covers 100% of parameters, so the baseline is 3. The description adds value by clarifying how the optional 'concept' parameter changes the response and by providing concrete examples of valid concept values. The 'identifier' parameter semantics are also clearly described in the schema.

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 states a specific action and resource: retrieving structured XBRL financial facts for a company. It also distinguishes two clear modes based on whether 'concept' is provided, making the tool's purpose and scope immediately understandable.

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 clearly explains when to use the tool with and without the 'concept' parameter, giving explicit invocation context. It does not explicitly name sibling tools or say when not to use it, but the structured data framing makes the intended use evident.

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