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

Annotations already provide readOnly, idempotent, and non-destructive hints. The description adds useful behavioral and operational context: it names the data source, states that no authentication is required, and enumerates the returned auction/issuance fields, all without contradicting the annotations.

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 compact and front-loaded: purpose first, then returned fields, then a helpful CUSIP hint and source attribution. Every sentence contributes useful information without redundancy 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?

For a single-parameter lookup tool with a rich output schema and safety-related annotations, the description is complete. It explains what is returned, where the data comes from, and that no auth is required, so an agent has what it needs to select and invoke the tool correctly.

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 single cusip parameter is fully described in the schema, including the '912797TW7' example. The description repeats the CUSIP prefix hint but does not add meaning beyond what the input schema already provides, so the baseline score of 3 applies.

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 clearly states the action ('Look up a specific US Treasury security by its CUSIP identifier') and names the exact resource. It also lists the returned data fields, making the tool's purpose unmistakable and distinguishable from the auction/rates siblings like treasurydirect.auction.results.

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?

The description clearly indicates this is for lookup of a specific security when a CUSIP is known, which gives an agent the context to select it. It does not explicitly name alternative tools or state when not to use it, but the 'specific ... by its CUSIP' framing is sufficiently clear.

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