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

Annotations already cover the safety profile (readOnly=true, destructive=false, closed-world), so the bar is lower. The description still adds real value on top: cost ('FREE'), the passage length cap (≤300 chars), and the ?ref=mcp attribution behavior on every URL — none of which the annotations convey.

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?

Three tight sentences front-load the return shape, then the argument constraint, then cost and tracking. No wasted wording; the bracketed capability/mirror metadata is compact and useful for provenance.

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?

An output schema exists, so return values need not be explained. The description covers scope, argument constraint, cost, and URL behavior, which is enough for a read-only lookup with 0 required parameters. Only the limit parameter goes unaddressed.

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?

Coverage is 67% and the description's parameter-relevant contribution ('exactly one of emotion or theme') largely duplicates the schema's mutual-exclusion notes. It says nothing about limit, its 24 default, or its 24 ceiling. Adequate but not additive.

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 concrete resource and its shape: a reading list for an emotion or theme page, returning books with one-line claims and short attributed passages. That is far more specific than a restated name. It does not, however, distinguish itself from the many vela.corpus siblings, so a 5 is not warranted.

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 one hard rule given is 'Exactly one of emotion or theme', which tells the agent how to supply arguments. But there is no when-to-use guidance, no pointer to a sibling for the alternative (e.g. list_topics or query) and no indication of when this source is preferable. Usage is implied rather than taught.

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