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

Annotations already indicate this is a mutating operation (readOnlyHint=false) and not idempotent, so the description does not need to restate that. It adds one useful behavioral rule: 'One currency per account.' However, it does not disclose side effects such as whether the account is immediately usable, how opening_balance interacts with account creation, or any validation failure behavior. The added constraint earns some credit but the transparency is thin.

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 very short, with no filler or redundant elaboration. The core action is front-loaded and the currency constraint follows directly. It is concise, but it is also minimal to the point of omitting valuable guidance, which keeps it from a 5.

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?

With 8 parameters, 3 required fields, enum values, and an output schema, the description only states the action and one constraint. It leaves the agent to infer required fields, account type options, and the significance of opening_balance. While the schema and output schema provide some structured context, the description does not fill the gaps for a non-trivial creation operation.

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 only 50%, so the description must compensate for undocumented parameters. It does not. The only semantic guidance is 'One currency per account,' which partially explains the currency parameter. It says nothing about name, type, opening_balance, as_of, last4, region, or institution. The schema itself documents a few fields, but the description adds no meaningful parameter-level detail beyond the currency constraint.

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 states the specific verb and resource: 'Create an account.' The added constraint 'One currency per account' gives a meaningful business rule that differentiates the act of creation from generic setup. It is not a tautology, though it relies on the tool name for the core action. It clearly distinguishes from sibling tools like update_account and set_account_balance, which imply modification rather than creation.

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 gives no guidance on when to use this tool versus alternatives such as list_accounts, update_account, or set_account_balance. It does not mention prerequisites, typical scenarios, or when a user should call a different tool. The usage context is only implied by the word 'create' and the sibling list.

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