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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description does add one genuinely useful behavioral note: the cost is opaque/not in the public credit manifest, which warns the agent not to assume pricing. It adds nothing about response shape, but an output schema exists to cover that.

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?

One short sentence followed by two bracketed metadata tags; nothing is wasted and the core purpose is front-loaded. Slightly terse rather than padded, which is the right direction.

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 by-slug lookup with a full output schema and annotation coverage, the description plus structured fields are nearly sufficient. The remaining gap is sibling disambiguation against `astroway_tarot_marseille_spreads` and `astroway_tarot_rider_waite_spreads_slug`, which the description does not address.

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%: the `slug` format (lowercase, hyphenated), the compact `fields` paths, and `precision` rounding are all documented in the schema. The description adds no parameter-level meaning beyond that, so the 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?

States a specific verb-ish noun phrase: it returns the definition of a single Marseille spread. Combined with the title and the `slug` parameter, an agent can infer it is a by-slug lookup. However, it never distinguishes itself from the sibling `astroway_tarot_marseille_spreads` (the list variant), so the intended scope is only implied by the `_slug` suffix.

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?

No when-to-use guidance at all. The description does not say to call this once a spread slug is known, nor does it point to `astroway_tarot_marseille_spreads` as the way to discover valid slugs. The agent must infer the workflow from naming conventions alone.

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