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

Annotations already declare destructiveHint=true and idempotentHint=true, so the safety profile is known. The description adds valuable behavioral detail beyond annotations: null clears fields, archived hides history, annualRatePercent turns the account interest-bearing, and the currency restriction. No contradiction with annotations.

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?

A single, dense paragraph with no filler. The core action is front-loaded, and each clause adds distinct information. It avoids restating schema details, focusing only on behavior.

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 15-parameter schema and low description coverage, the description covers the most critical behaviors (null semantics, archiving, currency constraint, interest terms). The presence of an output schema reduces the need to explain return values. However, it omits behavior for fields like kind and openedOn, which might require inference, but overall it is sufficient for an agent to make correct update calls.

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 low at 40%, so the description carries extra weight. It explains the semantics of null for institution, last4, note, creditLimit, and annualRatePercent, and clarifies the currency change restriction. However, it doesn't address parameters like kind, name, openedOn, includeInNetWorth, leaving some ambiguity, but the description compensates meaningfully for the coverage gap.

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 opens with 'Changes an existing account' – a specific verb and resource. It then enumerates the mutable fields and clarifies scoping (only passed fields change), which clearly separates it from create_account and delete_account. The mention of list_accounts for IDs further distinguishes the update workflow.

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?

While it doesn't explicitly say 'use this instead of create/delete', it provides a concrete usage rule: currency can only change when no transactions exist, and IDs come from list_accounts. This gives agents actionable constraints. It could be improved by explicitly stating 'for new accounts use create_account', but the context is reasonably clear.

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