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

Beyond the readOnly/openWorld/idempotent annotations, the description discloses detailed behavior: it computes transiting planet positions at target_datetime, all aspects to natal points including angles, exact orbs, applying/separating states, natal house placement per transiting planet, and embeds the full natal chart. This gives the agent a clear model of what the tool does internally without contradicting annotations.

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, front-loaded with the usage directive and followed by a compact feature list. Every clause earns its place—no filler, no repetition of schema details, and the most important guidance comes first.

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 fairly complex astrological computation with no output schema, the description covers what is computed, which points are included, and what extra data is embedded (houses, full chart). It does not describe the exact response structure or pagination/format details, but for the agent's invocation decision the description is reasonably complete.

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%, so the baseline is 3; the description adds meaning beyond field names by explaining how target_datetime is used ('transiting planet positions at target_datetime') and how natal relates to it ('every aspect ... to the natal points ... with the natal point fixed'). This helps an agent understand which parameter drives which behavior, though the schema already documents the basics well.

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 verb+resource ('compute transits to a natal chart') and immediately ties it to concrete user intents: 'what is going on for me now / today / this week / this month', horoscopes, forecasts, and transit questions. This clearly distinguishes it from siblings like calculate_natal_chart (static chart) and calculate_synastry (relationship chart).

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 says 'Use this tool for ANY ... forecast or transit question' and instructs the agent to 'never estimate transiting positions yourself and never web-search them', giving strong when-to-use guidance. It does not explicitly name alternative sibling tools or state when NOT to use them, stopping just short of a 5.

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