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

Although the description discloses useful behavioral details like empty-string clearing and automatic EquityValuation creation, it directly contradicts the `idempotentHint: true` annotation. The description says that sending `value` and/or `cost` registers a new EquityValuation dated now, so repeated identical calls would create multiple valuations. This is a non-idempotent side effect, making the description contradict the annotation.

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 compact and well structured. It leads with the core action, then explains edge-case behavior, then closes with the alternative tool usage. Every sentence earns its place, and there is no redundant or filler content.

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 complex mutation tool with 11 parameters and side effects, the description covers the key operational details: field update semantics, empty-string clearing, automatic valuation behavior, and when to choose the sibling tool. An output schema exists, so return-value details are not required. The unresolved contradiction with `idempotentHint` prevents a perfect completeness score, but that issue is already counted under behavioral transparency.

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 meaningful semantics beyond the schema: omitted fields retain their current value, empty strings clear certain fields, and the implicitly created valuation is dated now with no retroactive date. There is a minor inconsistency where `shares` is listed among string-cleared fields even though its schema type is number, so a perfect score is not warranted.

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 action: updating fields of an existing investment identified by `id`. It also distinguishes itself from `add_equity_valuation` by explicitly noting the difference between implicit current-date valuation and historical valuation. This is specific, unambiguous, and differentiates the tool from its siblings.

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?

The description explicitly tells the agent when to use `add_equity_valuation` instead: when recording a historical value on a specific date without changing other investment fields. It also implicitly conveys that `update_equity` is the right choice for updating existing investment fields and optionally recording a current valuation. This is strong routing guidance.

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