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

Annotations already declare readOnlyHint and idempotentHint, so the safety profile is covered. The description adds behavioral details beyond those: Form 477 periods are hardcoded and always available, while BDC periods come from an authenticated API requiring credentials. It also notes a data gap between the two sources. These add context that enriches what the annotations already imply, 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 a single sentence that packs all essential information: what is returned, the time ranges, authentication needs, and a reference to the sibling tool. It is front-loaded with the core purpose ('Returns available data vintages') and each clause earns its place. There is no redundant wording or filler.

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?

The tool has an output schema, so return format is already documented. The description covers the main use case (determining as_of_date values for fcc_list_downloads), the data sources, and the gap. It doesn't mention error handling or performance, but these are not critical given the constraints. It is sufficiently complete for an agent to call the tool correctly, though it could include a note about the impact of include_bdc on performance or authentication failures.

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 coverage is 100%, and the description's mention of 'requires credentials' overlaps directly with the schema's parameter description for include_bdc, which already names FCC_BDC_USERNAME and FCC_BDC_HASH_VALUE. The description adds no new meaning about the parameter beyond the schema, though it does contextualize the data gap. This meets the baseline for good schema coverage but doesn't exceed it.

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 verb ('Returns'), a precise resource ('available data vintages'), and enumerates the two types (Form 477 filing periods and BDC as-of dates). It explicitly names the sibling tool fcc_list_downloads, establishing clear differentiation and scope. There is no ambiguity about what this tool provides.

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 directive: 'Call this before fcc_list_downloads to determine valid as_of_date values.' This tells the agent exactly when to use the tool and why. It also notes the authentication requirement for BDC periods, which informs the caller about prerequisites. The mention of the data gap adds context about timing, though it doesn't list explicit exclusions for when not to use it, the guidance is strong enough for a 5.

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