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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds a genuinely useful behavioral fact not in the schema: the 10-credit Tier 1 cost. It says nothing about how non-alphabetic characters or accents are handled, which is the main ambiguity for a name-letter calculation.

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 core sentence is front-loaded and wastes no words; the calculation rule is stated in one parenthetical. The bracketed Group/Cost lines are boilerplate but carry real information.

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 no explanation, and the cost is disclosed. However, the unexplained required 'date' parameter and the total absence of when-to-use guidance leave gaps for a tool sitting among dozens of near-identical Expression siblings.

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 50%: 'fields' and 'precision' are documented in the schema, while 'name' and 'date' are bare. The description hints that 'name' must be the full birth name (all letters counted), which partially compensates, but it never explains why a date is required for an Expression number that is derived from name letters alone.

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 gives a specific verb ('Calculate'), a named resource ('Expression (Destiny) number'), and the exact input rule ('full birth name letters, all letters, reduced'). Naming 'Chaldean system' separates it from the pythagorean/kabbalistic/vedic Expression siblings, though it relies on the group tag rather than an explicit contrast.

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 statement of when to choose Chaldean Expression over, say, astroway_numerology_pythagorean_expression or astroway_numerology_chaldean_soul_urge. The agent is left to infer selection purely from the system name embedded in the tool name.

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