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 adds genuinely new behavioral context: the data is static, drawn from fixstars.cat, the 36-star astrological default set is flagged in the output, and it costs 5 credits. That is meaningful disclosure beyond the structured fields, though it omits response shape or pagination details (partly covered by the output schema).

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 dense, front-loaded sentence plus three bracketed metadata lines (group, endpoint, cost) that all carry actionable information for the agent. No filler; slightly heavy packing of five output fields into a single clause, but nothing is wasted.

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 re-explained, yet the description still enumerates the catalog columns. Combined with the cost, endpoint, and 'no chart needed' note, an agent has everything required to select and invoke this reference tool correctly.

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% for the two declared parameters (fields, precision), so the schema does the heavy lifting and baseline is 3. Notably the description introduces an '?maxMagnitude=' trim option that does not appear in the input schema, which adds information but also creates ambiguity about whether it can be passed as a tool argument or only as a raw query string.

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 concrete resource and scope: the star names the API accepts, sourced from Swiss Ephemeris fixstars.cat, with the exact fields returned (traditional name, Bayer nomenclature, constellation, magnitude, default-set flag). It also implicitly separates itself from the chart-based sibling astroway_aspects_fixed_stars via 'Static lookup, no chart needed', though it never names that sibling explicitly.

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?

Usage is only implied: 'Static lookup, no chart needed' tells the agent this is a prerequisite/reference call rather than a computation, and the maxMagnitude note signals a filtering option. There is no explicit statement of when to call this versus astroway_aspects_fixed_stars or astroway_geo_parans_star, so the agent must infer the routing.

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