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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and a closed world, so the safety profile is covered. The description adds genuinely useful operational context in the credit cost and tier, but says nothing about determinism, error behavior, or what the computation does when the name contains non-letter characters.

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 short sentences with the verb+resource front-loaded, followed by the system qualifier. The bracketed group and cost lines are compact metadata rather than prose padding, so little is wasted, though the cost/group lines arguably belong in structured fields.

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. The remaining gaps are the unexplained required 'date' parameter and the absence of any distinction from the non-strict Kabbalistic sibling, but for a single-purpose calculation tool the description is close to sufficient.

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 50%: 'fields' and 'precision' are documented in-schema, while 'name' and 'date' are not. The description partially compensates by clarifying that 'name' means the full birth name with all letters counted, but it never explains why a 'date' is required for an Expression calculation or how it is used.

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 names a specific verb and output (calculate the Expression/Destiny number) plus the resource it derives from (full birth name letters) and the system (Kabbalistic, Mathers strict). It implicitly separates Expression from soul_urge/personality via 'all letters, reduced', but never contrasts itself with the non-strict sibling astroway_numerology_kabbalistic_expression, which shares almost the same name.

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?

There is no explicit when-to-use, when-not-to-use, or alternative selection guidance. The system label ('Kabbalistic (Mathers strict)') implies the agent should pick this only for strict Mathers calculations, but that inference is left entirely to the caller despite several near-identical siblings.

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