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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds real content beyond that: it discloses the computation source (Swiss Ephemeris) and that the result bundles a written reading plus recent Q&A, which tells the agent the call is heavier than a bare placement lookup. It does not say what happens if no chart exists or the chart_id is unknown.

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 sentences, front-loaded with the return payload and ending with the actionable usage rule. No filler, no restatement of the title.

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?

With no output schema, the description carries the burden of describing the return value, and it does so concretely (placements, personal reading, latest Q&A). What is missing is edge-case behavior for a zero-required-parameter tool: what is returned when the user has no saved chart, and how 'latest' Q&A is bounded.

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 coverage is 100%, so both parameters (lang, chart_id) are already documented, including the 'omit for the first (own) chart' default. The description adds only indirect context ('signed-in user', 'without asking for birth data') and no new detail on lang or chart_id semantics. Baseline 3 applies 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?

The description names a specific verb and resource ('Returns one saved chart of the signed-in user') and enumerates the payload: natal placements, the AstralRead reading, and latest Q&A. The phrase 'without asking for birth data' implicitly separates it from chart-construction siblings like natal_chart, and 'one saved chart' vs the plural my_charts sibling.

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?

It gives a clear use case: 'Use it to answer questions about the user's own chart without asking for birth data.' That is a strong positive routing signal. It stops short of naming an alternative or stating when not to use it (e.g., when the user has no saved chart, or wants another person's chart).

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