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

Annotations already provide read-only, idempotent, and non-destructive hints, so the bar is lower. The description adds valuable context about the frozen archive, what the date covers, and the limitation that it is not an arbitrary per-fund figure on an arbitrary day. It does not describe return format, but that is minor for a simple read-only lookup.

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?

Three sentences, each with a clear job: what the tool does, when to use it, and how the date parameter behaves. The most important usage guidance is front-loaded and there is no 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?

For a tool with one simple parameter and no output schema, the description covers purpose, usage conditions, and date format thoroughly. The only slight gap is that it does not explicitly describe the shape of the returned content, but 'what ETFIQ published' gives enough context for likely use.

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 schema only says the date parameter is a string with 0% coverage, so the description must compensate. It does so by specifying the exact format 'YYYY-MM-DD' and explaining what the date means in relation to the frozen archive. This fully resolves ambiguity.

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 specifically that the tool returns 'what ETFIQ published on a given date' from its 'frozen dated archive.' It also distinguishes itself from siblings by noting that other tools answer about today, making it instantly clear where this tool fits.

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 direct usage conditions: 'Use when a question is about a past date, or when a figure needs to stay true after it is quoted.' It also explains why alternatives are less appropriate because they answer about today and 'today moves overnight.'

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