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

Annotations declare readOnlyHint=true; the description adds 'Free + rate-limited' and 'NO key required', giving context on auth and rate limits beyond the annotation. It doesn't describe error handling or rate-limit behavior, but the added details justify a 4.

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 'Zero setup — NO key required' and the core return details, but the second sentence about signing up for a Discovery key is somewhat promotional and could be trimmed. Still, it's not overly long and every sentence serves some purpose.

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 simple one-parameter lookup tool with an output schema, the description covers purpose, usage, auth, rate limits, and source/link return. It doesn't need to explain return values since the output schema exists, making it complete in context.

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 already provides 100% coverage for 'q' with the same examples (e.g., 'high blood pressure', 'sleep'). The description repeats these examples but adds no new parameter meaning, so it fits the baseline for full schema coverage.

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 states a clear verb+resource: 'Returns ONE already-public federal health fact, list, or tip' with source and link. It distinguishes the lookup from sibling stream/message tools by emphasizing zero setup, no key, and public content.

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 explicitly says 'Zero setup — NO key required' and points to an alternative (Discovery key) for adaptive, patient-specific sequencing. However, it doesn't explicitly state 'when not to use' or name sibling tools, so it's clear but not exhaustive.

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