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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is fully covered by structured fields. The description adds real behavioral value beyond that: it discloses the shape of the return (covered periods with per-period submission/fact/note-block counts) and its intended diagnostic role, which matters since there is no output 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?

Two tightly written sentences: the first states what is returned, the second states when to call it. The diagnostic advice is front-loaded and no sentence is padding.

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 input parameters and no output schema, the description carries the burden of explaining the return, and it does so at a high level (periods plus counts). It could be marginally stronger by sketching the response format, but nothing essential for a correct zero-arg call 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?

The tool takes zero parameters, so per the rubric the baseline is 4. There is nothing for the description to clarify about inputs, and it does not attempt to invent any.

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 names the specific resource (SEC Financial Statement & Notes periods), the two payload dimensions returned (coverage plus submission/fact/note-block counts), and frames the tool's role as a diagnostic. It doesn't explicitly contrast itself with siblings like company_financial_facts, but the coverage-check framing is specific enough to distinguish it in practice.

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 a clear trigger condition: 'Call this first if a lookup returns nothing, to confirm whether the period you need is actually covered.' That is concrete when-to-use guidance. It stops short of naming which alternative lookup tools it disambiguates against, so no explicit exclusions.

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