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

Annotations already establish safety (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds real behavioural context: the bundled GeoNames set is 34,028 places above 15,000 people, and supportive and challenging totals are returned separately with each contributing line and its distance. It does not cover rate limits or auth, but the search-space scope is genuinely valuable and not derivable from annotations.

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 leading sentence is well front-loaded, but the second sentence spends substantial length on spherical-geometry mechanics ('the distance to a horizon line IS the altitude in degrees of arc, and a meridian line offset is the hour angle times cos(latitude)') that does not help an agent decide to call the tool or how to invoke it. The dataset-size sentence does earn its place.

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 spelled out, and the description still adds ranking semantics and dataset scope. Combined with a 100%-covered schema that points to GET /v1/acg/categories for valid category values, an agent has what it needs. Only the sibling differentiation gap keeps it from being fully complete.

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 the schema already documents category, sort, orbKm, minSeparationKm, limit, countries and precision in detail. The description adds no parameter-level syntax or defaults beyond what the schema provides. Baseline 3 applies when structured fields carry the full parameter burden.

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 verb and resource: 'Rank cities against the astrocartography lines of a chart for one of the 19 life categories.' An agent immediately knows this returns a ranked city list for an ACG life category. It does not, however, distinguish itself from the very similarly named sibling astroway_geo_acg_by_category, so the sibling differentiation half of the criterion is unmet.

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 explicit when-to-use guidance and no mention of alternatives, despite several close siblings (astroway_geo_acg, astroway_geo_acg_by_category, astroway_geo_acg_zones). The 50-credit Tier 3 cost is disclosed, which is useful for budgeting, but nothing tells the agent whether to reach for this tool or a cheaper sibling. Usage is only inferable from the description of what gets returned.

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