Calculate a chart without a birth time

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

With no annotations provided, the description fully carries the behavioral burden. It discloses that omitted chart points are not estimated, that only genuinely knowable data is returned, and that the Moon sign may be reported as undetermined when the Moon changed sign that day. This goes well beyond a generic 'calculate' description.

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?

Four sentences, with the target audience front-loaded and every sentence contributing a distinct, useful behavioral fact. There is no filler or repeated schema information, and the description remains readable despite covering nuanced caveats.

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?

Despite having no output schema, the description clearly communicates what the tool returns and what it deliberately omits, along with the Moon-sign uncertainty and the no-fabrication policy. Combined with the fully documented input schema, an agent has enough context to select and invoke the tool correctly.

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%, and the schema already documents all four parameters, including the important timezone caveat about birthplace versus user's current zone. The description adds context about date sensitivity for the Moon sign but does not need to repeat parameter-level syntax.

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 states a specific use case: calculating a chart when birth time is unknown. It distinguishes itself from a normal natal-chart calculation by explicitly naming what is omitted (ascendant, midheaven, houses) and by warning against the common noon-substitution shortcut.

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 explicitly identifies the trigger condition: users who do not know their birth time. It also gives a clear exclusion by warning never to substitute noon and present the result as fact. It does not name sibling tools explicitly, but the intended usage is unambiguous from context.

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