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

Annotations already establish readOnly, idempotent, non-destructive, and closed-world behavior. The description adds meaningful context: counted aspects only, no compatibility score, nothing stored, and concrete return categories. It does not cover auth or rate limits, but for a read-only calculator it is solid.

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 purpose, then enumerates the return contents, then closes with two short caveats. Every sentence earns its place and there is no filler.

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 two-parameter nested-object tool with no output schema, the description supplies the missing return-value picture and the key limitation that there is no compatibility score. Annotations and schema cover safety and input details, so nothing critical is absent.

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%: the nested personA/personB objects, date/time/place constraints, and unknown-time handling are already fully documented. The description only says 'from their birth data' and adds no parameter meaning beyond the schema, so baseline 3 applies.

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: compare two people's charts (synastry) from their birth data. The two-person framing clearly distinguishes it from natal_chart, and the description names the output domain immediately.

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?

Usage is implied by 'Compare two people's charts (synastry)' and the birth-data scope, but it never explicitly says when to choose this over natal_chart or search_places, nor any exclusions. The 'no compatibility score' statement sets expectations but is not routing guidance.

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