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

The description adds behavioral context beyond the readOnlyHint annotation by explaining the signal's interpretation (50=neutral, >50=more inverted), computation (z-scored vs trailing window), output components, and update frequency ('Updates: monthly'). It also notes the Gold tier requirement for history, though that is also in the schema. This is valuable but not exhaustive.

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 three sentences, front-loaded with the core output and meaning, followed by precise usage guidance and update frequency. Every sentence adds value without redundancy, making it highly efficient for an AI agent to parse.

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?

The description covers the tool's purpose, output components, scale interpretation, usage triggers, and update cadence. While there is no output schema, the description lists the returned fields (trend, confidence, inversion_depth_label, raw spreads, composite_z). Minor gaps include exact definitions of trend/confidence and the history behavior, but the schema covers the parameter, and the description is adequate for most agent interactions.

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 'days' is fully described in the input schema (coverage 100%), including its optional nature, range, and the Gold tier requirement. The main description does not mention 'days' at all, so it provides no additional semantic meaning beyond the schema. Thus the baseline of 3 is appropriate.

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 specific function: 'Returns a 0-100 yield-curve inversion signal' with detailed methodology and output fields. This distinguishes it from generic siblings by focusing on the unique yield-curve inversion signal, making it easy to identify when this tool is relevant.

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 provides explicit use cases: 'Call when the user asks about yield-curve inversion, 10y-2y or 10y-3m Treasury spreads, curve flattening/steepening, or recession risk, or when timing credit de-risking, duration, or cash-allocation decisions.' It does not mention when not to use or name alternatives, which prevents a 5, but the guidance is specific and helpful.

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