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 genuine context beyond that: the charts come from an independent source, are fixed rather than computed, and the harness edge cases they exercise.

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?

Front-loads the core purpose and uses labelled WORKFLOW / INPUT CONTRACT / DO NOT CONFUSE WITH sections that are easy to scan. The long parenthetical list of edge cases is slightly verbose, though it does inform what the returned data contains.

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?

For a read-only, zero-required-input listing tool with a full output schema and rich annotations, the description covers everything an agent needs: purpose, placement in the workflow, the sibling to compare against, and a link to the full output/error contract.

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?

Only one parameter (response_format) with 100% schema description coverage, so the schema already documents it fully. The 'INPUT CONTRACT: No inputs beyond response_format' line is consistent but adds no meaning beyond what the schema states.

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 — published test charts with reference values — and enumerates exactly what they cover. The 'DO NOT CONFUSE WITH' section explicitly separates it from asterwise_get_natal_chart, so an agent can distinguish it without opening a schema.

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?

Gives explicit workflow: standalone with no prerequisites, then a follow-up step of sending an input to asterwise_get_natal_chart to compare. Names the alternative and the condition ('this lists charts to check it against'), leaving nothing to inference.

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