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

Beyond the read-only/idempotent annotations, the description discloses key behavioral details such as 'spread_pos (1-14 canonical Life-spread order; midheaven=13, phoenix=14 — sort by spread_pos; jsonb object keys are unordered)', the temporal_context band/payload_scope, and out-of-range behavior setting cosmic_card_available. These are non-obvious behaviors not inferable from 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?

The description is long and dense, but every section contributes value. It is front-loaded with the primary use case and exclusions, then systematically enumerates return blocks and special attributes. The extensive name list (greek, norse, celtic, etc.) makes it verbose but is necessary given the lack of output schema.

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 tool with no output schema and high complexity, the description is remarkably comprehensive. It enumerates all major return blocks (cosmic, tarot_majors, day_ruler, temporal), details nested structures like planetary_spread and retrogrades_active, explains sorting requirements (spread_pos), and covers edge cases like out-of-range. This gives the agent sufficient information to invoke the tool and interpret results.

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% for the single 'date' parameter, providing format and pattern. The description adds semantic context about what dates are valid ('any Gregorian date') and describes out-of-range response behavior, which slightly exceeds the schema baseline but does not introduce new parameter 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 clearly states the tool's purpose: 'PRIMARY single-date tool' that returns comprehensive date identity data (moon phase, season, retrogrades, calendars, etc.). It explicitly distinguishes itself from siblings with 'NOT for two-person scoring → get_compatibility; name text → get_name', making the scope unmistakable.

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?

Usage guidance is explicit: 'USE for any one Gregorian date when the ask needs...' followed by a detailed list of triggers. It also provides clear exclusions and alternative tool names, which is exactly what an agent needs to select the right tool.

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