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

Annotations already declare the safety profile (readOnly, non-destructive, openWorld, non-idempotent), and the description usefully adds context beyond that: a 10-turn history cap, 21 supported languages, four persona voices, and a cost behavior where sending your own provider key drops the turn to 5 credits. It stops short of describing failure modes or what the chart object must contain to succeed.

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?

Three tight sentences, front-loaded with the core differentiator ('answered from the positions we computed') before secondary facts about history, languages, and pricing. The trailing group/cost tags are metadata rather than prose, so there is minimal waste.

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 explained, and the description covers the AI-behavioral surface (grounding, history, language, persona, cost). For a 7-parameter tool with nested objects and low schema coverage, it could say more about the chart input contract, but the essentials are present.

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 only 43%, so the description should compensate, and it partly does by explaining history (10 turns), language (21), and persona (four voices). However, it says nothing about the required `message`, the complex nested `chart`, or the compact-mode `fields`/`precision` parameters, leaving those to the schema.

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?

The description states a specific verb and resource — a chat grounded in computed chart positions rather than the model's sun-sign memory — which is clearly distinguishable from report-generation siblings. It does not explicitly name an alternative among the many AI siblings (explain_aspect, explain_transit, comparison_coach), so it falls short of a 5.

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?

The description explains what the tool is but never says when to reach for it versus the other AI siblings or the narrative-report tools. No prerequisites or selection conditions are given; the agent must infer usage from the name alone.

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