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

Annotations already declare readOnly, idempotent, non-destructive and openWorld=false, so the safety profile is covered. The description adds genuinely useful non-annotation context: the cost (50 credits, Tier 3), the endpoint, and the fact that output is 'a timeline of directed aspect hits'. It says nothing about rate limits, auth, or the effect of the key/rate choice on results.

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 compact sentences plus bracketed metadata lines; the core purpose and the return shape are front-loaded with no filler. The group/endpoint/cost lines are functional rather than padding, though the endpoint adds little for an agent that already has the tool.

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-value detail is unnecessary, and the cost is disclosed. The main gap is disambiguation: in a Prognostics family with a dozen timing techniques, the description never tells an agent why primary directions rather than symbolic directions or progressions is the right call.

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% and the nested body schema fully documents date/time/latitude/longitude, timezone, houseSystem and the key/maxAge/aspectAngles group. The description only loosely maps to maxAge ('up to a maximum age'); it never explains the key parameter's degrees-per-year semantics. Baseline 3 is appropriate when the schema does the heavy lifting.

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?

Names a specific verb and resource ('Calculate primary directions') and scopes it with the method variants (Ptolemaic/Regiomontanus) and the 'up to a maximum age' bound, which matches the maxAge parameter. It does not explicitly distinguish itself from close siblings like symbolic_directions or progressions, so an agent must still infer which direction technique fits.

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 primary directions versus the many other prognostic siblings (firdaria, profections, symbolic_directions, transits). No prerequisites, no exclusions, no named alternative — the agent gets no routing help in a crowded Prognostics family.

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