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

Annotations already establish readOnly, idempotent, non-destructive, and closed-world behavior, so the safety profile is covered. The description adds the method variants and that output is a timeline of aspect hits, but says nothing about cost implications beyond the tag, computation weight, or what the 'key' rate selects.

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 sentences, front-loaded with the action and the return value, with no filler. The trailing group/cost tags are metadata rather than prose, so the core text is tight, though the description is arguably too terse for a Tier 3 niche technique.

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?

Because an output schema exists and annotations cover the safety profile, the definition does not need to explain return values or side effects. What remains missing is routing guidance among numerous prognostics siblings and any hint about the direction rate/method selection, making it minimally adequate for a specialized tool.

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 body, fields, precision, maxAge, key, and aspectAngles in detail. The description only loosely gestures at maxAge ('up to a maximum age') and does not clarify the Ptolemaic/Regiomontanus distinction against the numeric 'key' rate parameter, so it neither adds nor detracts much.

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 and resource ('Calculate primary directions'), names the two supported method variants (Ptolemaic or Regiomontanus), and gives the scope ('up to a maximum age') plus the return shape. It does not, however, distinguish itself from closely related siblings such as symbolic_directions or minor_progressions, so an agent must already know the difference between primary and symbolic directions.

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 when-to-use guidance, no prerequisites, and no named alternative among the many prognostics siblings. The phrase 'up to a maximum age' hints at a scope limit but never tells the agent how to choose this tool over transit_calendar, progressions, or symbolic_directions.

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