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), so the bar is lower. The description nonetheless adds a genuinely useful trait beyond them: 'Unknown fees are flagged, never assumed,' telling the agent how missing data is surfaced rather than silently imputed.

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 tightly packed sentences that front-load the purpose before the data-quality caveat. The parenthetical fee list is dense but each item maps to a real cost dimension, so little is wasted.

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 described, and the schema documents all five parameters with defaults. The description covers scope, cost components, and unknown-fee handling; only the relative role of inputs versus alternatives is left implicit.

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, and the description adds a little on top by tying parameters to the fee model ('options per-contract', 'transfer-out', 'exchange taker fees'). It stops short of explaining how inputs like trades_per_month or transfers_per_year combine, leaving that to the schema.

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?

Specific verb ('Estimate') plus resource ('annual cost') and an explicit scope ('every brokerage or crypto exchange VaultRubric tracks'), with the cost model components enumerated. This is clearly distinguishable from siblings like compare_platforms or get_verdict that answer different questions.

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?

Implied usage is clear (cost projection to support a platform decision), but there is no explicit when-to-use, when-not-to-use, or named alternative such as compare_platforms. The agent must infer the routing from the scope sentence alone.

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