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

Annotations already declare a safe, idempotent, closed-world read, and the description adds substantial context beyond them: a hard 12-value cap, newest-first ordering, revision marking, a licensing restriction (Terms §7B), the fact that each value carries period/retrieval date/source, and an attribution obligation. It also warns that coverage labels can change the meaning of figures (I-94 example), which is real behavioral guidance an agent would otherwise miss.

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 lead sentence is well front-loaded and information-dense, but the tail drifts into boilerplate ('Facts, not investment or other advice') and licensing citations that consume space without helping selection or invocation. The valuable coverage-label warning is buried mid-paragraph rather than surfaced early.

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 output schema, the description does the necessary work of describing the return shape: per-value period, retrieval date, source, and revision flags. It is nearly complete for a simple single-parameter read, with only error or empty-result behavior left unspecified.

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 single parameter has 100% schema coverage including an example format, so the schema carries the parameter burden. The description only reiterates 'one series' without adding format, validation, or sourcing detail beyond what the schema already states.

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 first sentence names a specific verb and resource ('Up to 12 most recent values of one series, newest first, one per period') and adds scope details like revision marking. It never names or distinguishes itself from the sibling 'latest', which appears to be the closest alternative, so an agent cannot fully disambiguate from the text alone.

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 states a scope exclusion ('Longer histories and as-of views are not part of the free door'), which tells the agent when this tool will not suffice. However, it gives no positive routing guidance toward 'latest' or 'search_series', and no prerequisites for obtaining a valid series_id beyond the schema's own example.

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