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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds a genuine behavioral note about billing ('see your plan — endpoint not in the public credit manifest'), which is useful cost context, but says nothing about lookup failure behavior or what the returned definition contains.

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?

Two short lines with the core purpose front-loaded, followed by group and cost metadata. Nothing is padded, though the metadata bracket lines are boilerplate rather than task-relevant guidance.

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 a full output schema and complete annotations, the structured data carries most of the burden, and cost context is provided. The gap is routing: with hundreds of siblings, including astroway_tarot_rider_waite_spreads and the Marseille equivalents, the description does not tell the agent which one to pick.

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?

Schema description coverage is 100%, so all three parameters (slug, fields, precision) are already documented with examples and constraints. The description only restates that lookup is by slug, adding no meaning beyond the schema; baseline 3 applies.

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 names the resource (a single spread) and the lookup key (slug), which implicitly separates it from the sibling astroway_tarot_rider_waite_spreads that lists all spreads. However, it uses a noun phrase ('Definition of...') rather than a verb, and never names the sibling it contrasts with.

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?

There is no statement of when to use this tool versus the list-style sibling, nor any prerequisite such as where a valid slug comes from. An agent must infer that slugs are obtained from astroway_tarot_rider_waite_spreads.

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