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

Annotations only state mutability (readOnlyHint=false) and non-idempotency. The description adds valuable behavioral detail: 'the rate is frozen at creation', 'Legs are excluded from spending', and 'an optional fee is a real expense'. These explain accounting effects that are not apparent from the schema. No contradiction with annotations; the extra context is significant but not exhaustive (e.g., no mention of balance updates or constraints on accounts).

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?

Three tightly written sentences, each carrying distinct information: the core action, the currency-handling nuance, and the accounting treatment. No filler or redundancy; all content earns its place.

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?

Given the tool's complexity (currency conversion, fee, leg accounting) and that an output schema exists, the description covers the most critical behaviors. It explains the rate freezing, spending exclusion, and fee expense—aspects that would otherwise be surprising. It omits minor details like whether from_amount is the source-currency amount, but these are inferable from the schema's required field and the 'source currency' note on fee. Overall, the description is sufficiently complete for correct invocation.

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 low (25%), so the description must compensate. It does clarify the roles of rate and to_amount ('For different currencies give to_amount or rate') and the fee ('an optional fee is a real expense'). However, it does not explain date, note, from_amount, or account IDs beyond what the schema's type/required fields imply. This partial compensation is helpful but incomplete.

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 'Move money between accounts' uses a specific verb and resource, clearly distinguishing this from create_account, delete_transfer, and log_transaction. The scope is explicit and unambiguous.

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?

Provides clear guidance for different-currency transfers: 'For different currencies give to_amount or rate; the rate is frozen at creation.' This tells the agent when to supply which parameters. It doesn't explicitly contrast with log_transaction for income/expense, but the purpose statement implies the use case, so the guidance is adequate though not exhaustive.

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