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

Beyond the read-only annotations, the description discloses the return object ('cosmic birth card + age_spread {age_civil, age_no, age_aliases, ...}'), date semantics ('completed civil years; no wall clock'), the leap-year edge case ('Feb-29 follows Postgres age()'), and the validation error ('as_of_before_birth when as_of_date < birth_date'). These are all behavior details the annotations alone do not provide.

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?

The description is front-loaded with the core use case, followed by focused exclusions, then the return shape and edge-case handling. Every clause adds information and there is no filler or redundant restatement of what the schema already 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 simple two-parameter, read-only, idempotent tool with no output schema, the description is materially complete: it specifies the output fields, date semantics, leap-year behavior, error condition, and sibling disambiguation. An agent can correctly invoke the tool without additional inference.

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?

The input schema is 100% covered with meaningful descriptions, so the baseline is 3. The description adds further semantic value: 'completed civil years', 'no wall clock', and the Feb-29 handling clarify how birth_date and as_of_date should be interpreted when computing age.

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?

Description starts with a specific verb-plus-resource: 'USE for one person's Magian Age Spread board seat' and lists the exact inputs. It explicitly differentiates from sibling tools by naming what it is NOT (90-year Long Range Journey theme, get_date sky/calendars, two-person scoring), so an agent can resolve it without opening the 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?

The description gives a clear when-to-use target ('one person's Magian Age Spread seat') and explicit when-not-to-use exclusions: not the 90-year Long Range Journey card, not get_date sky/calendars, and not two-person scoring. This is direct selection guidance against the sibling tools.

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