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

Annotations already indicate readOnly and idempotent, but the description adds substantial behavioral context: Rev 3 is advisory and not binding for DoD, the tool returns a withdrawal flag, and identifiers between revisions collide. This goes beyond the structured annotations 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 front-loaded with the core action and return list, then adds important caveats. The stats about 97 active requirements and objectives are extra but useful. It is slightly verbose but every section earns its place, especially the critical advisory warning.

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 compensates by listing what the tool returns (requirement statement, ODPs, objectives, withdrawal status). It also covers usage context and pitfalls. Minor gaps like error behavior or exact response format remain, but for a simple advisory lookup this is adequate.

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 input schema has 100% coverage of the single parameter, already explaining zero-padding and the Rev 2/Rev 3 identifier difference. The description reinforces this with an example and the collision warning, but does not add new semantic meaning beyond what the schema provides.

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 tool's function: 'Get one NIST SP 800-171 REVISION 3 requirement by its zero-padded number' and lists the exact contents returned (statement, ODPs, objectives, withdrawal flag). It explicitly distinguishes itself from lookup_control, which satisfies the sibling differentiation criterion.

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 gives explicit when-to-use and when-not-to-use guidance: 'Use lookup_control for anything contractual; use this when the user is planning ahead, doing civilian-agency CUI work, or has explicitly asked about Rev 3.' It also warns about identifier collisions between Rev 2 and Rev 3, providing clear decision-making context.

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