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

Annotations already declare readOnlyHint=true and idempotentHint=true; the description adds useful constraints: no API key required, 0.01 USDC/query, max 20 queries/session. This goes beyond annotations and clarifies pricing/rate limits 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 about 50 words and front-loads the key 'no key needed' message, but it repeats 'FREE preview — no key, no payment' after already saying no API key needed. The promotional tone and redundancy prevent a higher score.

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 tool with two optional parameters and no output schema, the description provides pricing, examples, and listing identity, but it never states what the response contains (e.g., a sample of matching public metadata). The schema description covers 'public metadata only,' but the main description alone is not fully self-sufficient.

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 documents both optional parameters (slug and question), so the baseline is 3. The description adds concrete sample question strings that map directly to the question parameter, which helps an agent formulate valid input.

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 identifies the resource (pubmedwatch listing) and the action (free preview, sample questions), so an agent can tell it's a preview tool. It lacks an explicit verb phrase like 'preview a data listing' and doesn't contrast with sibling query tools, so it isn't a 5.

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 tells when to call ('no API key needed', 'FREE preview') and suggests sample questions, but it never mentions when not to use it or names alternatives such as data_session_query. The usage context is implied rather than explicit.

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