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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world). The description adds materially useful operational context beyond that: endpoint, cost of 100 credits at Tier 4, and required fields. It still says nothing about output granularity (e.g. per-year vs per-day index values), which keeps it from a 5.

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?

One tight definitional sentence followed by bracketed metadata lines (group, endpoint, required, cost). Front-loaded and largely free of filler, though the metadata block partially duplicates the schema's required list.

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 need not be explained, and annotations carry the safety profile. However, for a 5-parameter tool with a 40% schema coverage, the unexplained 'pairs' argument and the undefined semantics of the year range leave real gaps for an agent to call it 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 only 40%. startYear and endYear are bare number/null with no schema description, and the description only restates them as required without explaining units, inclusivity, or valid range. The 'pairs' parameter is completely undocumented in both schema and description, so the description fails to compensate for the coverage gap.

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 (Calculate), a named resource (André Barbault Cyclic Index), defines it (sum of all outer planet separations), and gives its interpretive purpose (global crisis periods). This is distinguishable from the many sibling cycle/phase tools without opening any 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 phrase 'to indicate global crisis periods' implies why an agent would call it, but there is no explicit when-to-use, no condition selecting it over astroway_calendar_planetary_cycles or astroway_calendar_planetary_phases, and no exclusions. Usage is inferable but not guided.

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