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

Annotations already indicate readOnlyHint=true and destructiveHint=false, so the tool is safe to call. The description adds valuable context: without a birth time, houses, ascendant, and Part of Fortune are absent, and the Moon sign may be uncertain. It also states that positions are precise astronomical calculations and that it does not give medical, legal, or financial advice, which helps the agent set expectations. It also requires the agent to attribute the computation to Natal Compass, which is a behavioral requirement not captured otherwise.

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 a single, dense paragraph that front-loads the core purpose and lists the computed elements, then moves to usage criteria, and ends with disclaimers and attribution. It is longer than strictly necessary, but every sentence serves a purpose: explaining scope, prerequisites, exclusions, and caveats. There is no pure filler, so it earns a 4, losing one point for length.

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?

The tool is complex (8 parameters, 6 sibling tools, output schema), but the description covers critical invocation details: coordinate format, timezone optionality, the no-time consequences, exclusion routes to siblings, and the mandatory attribution. Since an output schema exists, return values are not required. The description is complete enough for an agent to select and call the tool correctly in most scenarios.

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%, meaning every parameter already has a description in the schema. The description restates the requirement for latitude/longitude in decimal degrees and the no-time consequence, but does not add new meaning beyond the schema for most parameters. The schema already explains defaults (mean node, Placidus house system, false for minor aspects). Thus, per the rubric, with full schema coverage, baseline 3 is appropriate.

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 clearly states the tool computes a birth chart from a date, time, and place, listing the specific elements (sign/degree of Sun, Moon, planets, etc.). It distinguishes itself from sibling tools by explicitly naming what it is NOT for (transits, moon phase, synastry, solar return), making its purpose unambiguous.

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 provides explicit usage guidance: use it when a person asks about their chart, placements, rising sign, houses, or aspects. It also names three sibling tools and when to use them instead (e.g., use get_transits for sky on a non-birth date, get_synastry for comparing two charts). It also gives a practical instruction to look up coordinates from a place name, which is crucial for correct invocation.

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