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

Annotations already establish read-only, idempotent, non-destructive, non-open-world behavior, so the bar is lower; the description still adds substantive context by disclosing that the series is derived from the serial when omitted and by bounding coverage to Series 1963+ Federal Reserve Notes. It also proactively rules out price and authenticity output, which prevents misuse.

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?

Purpose and output inventory are front-loaded, and the two trailing sentences carry the scope and exclusion limits with no filler. The opening sentence is a long, heavily comma-listed run-on, which slows parsing slightly but every clause adds 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?

With no output schema, the description correctly takes on the job of describing return content (patterns with exact odds, print-run counts, rarity band) and coverage limits, which is what an agent needs to call it. It stops short of describing the response shape or behavior on an invalid/unsupported serial.

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%, so the baseline is 3, but the description adds meaning beyond the schema: it clarifies that series is optional because it can be worked out from the serial, and it flags that denomination is required specifically for the star-note print run. That inference behavior is not stated in the schema itself.

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?

Specific verb+resource ('check a US bill's serial number') with a precise inventory of what comes back: FRB, series, every collector pattern with odds, and star-note print run details. It does not explicitly contrast itself with siblings like find_star_runs or list_serial_patterns, which overlap on the pattern/run territory, so an agent must infer the per-serial scope.

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 real scope limits for routing: 'Covers Federal Reserve Notes from Series 1963 on' and explicit exclusions ('no price and no authenticity judgement'), which tell the agent when this tool is the wrong choice. It never names an alternative sibling, so it falls short of full when/when-not/alternative guidance.

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