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

Annotations already cover read-only, idempotent, non-destructive, so the safety bar is met; the description adds genuinely new context by stating no account is needed and nothing is saved, and it describes what comes back (strongest connections plus a compatibilityUrl deep link). No mention of limits, accuracy caveats, or how missing birth times degrade the comparison, which would push it higher.

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 with the purpose front-loaded and the return value second; no filler. It could route to alternatives more tightly instead of spending words on the URL mechanism.

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 needn't be fully specified, yet the description still previews the key outputs. Combined with annotations covering safety and a fully documented nested schema, an agent has what it needs to call correctly; only the sibling differentiation is thin.

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% and the nested person objects are fully documented, so the schema does the heavy lifting. The description only echoes the field categories (names, dates, places, optional times) and omits the 'relationship' enum parameter entirely, adding nothing beyond 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?

States a specific resource (compatibility between two people) and the inputs it uses, which is clearly distinct from compute_birth_chart or get_reading. However, it frames the tool as 'compatibility' while the name/title say 'compare birth charts', and it never explicitly distinguishes itself from the sibling preview_compatibility, which appears to serve a similar purpose.

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 some implicit guidance ('if known' times, no account needed) but no statement of when to choose this over preview_compatibility or compute_birth_chart. The relationship between this tool and the compatibility-preview sibling is left to inference.

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