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

Annotations already declare destructiveHint=true and readOnlyHint=false, covering the mutating nature. The description adds the prerequisite of Id and SyncToken, which hints at optimistic concurrency, but it doesn't elaborate on consequences (e.g., permanent changes, overwriting behavior). Since annotations carry the safety profile, the description adds minimal behavioral context beyond that.

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 a single sentence with no filler. It front-loads the core purpose and includes the critical precondition (Id and SyncToken) in a concise parenthetical. Every word earns its place, and the structure is optimal for quick scanning.

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 rich schema that thoroughly documents the entity parameter (sparse updates, prohibited fields, etc.), the tool description does not need to repeat those details. It covers the essential prerequisite (fetching the currency to get Id/SyncToken) and implicitly signals the update workflow. A note about using create/delete for different operations would improve completeness, but the schema mitigates the gap.

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?

The input schema has 100% coverage with detailed descriptions for both 'entity' and 'company'. The tool description mentions 'requires Id and SyncToken', which is already included in the entity parameter's description. No new parameter-level information is added beyond the schema, so baseline 3 is appropriate.

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 ('Update'), the resource ('existing company currency'), and the target system ('QuickBooks Online'). It distinguishes from sibling tools like create_company_currency or delete_company_currency by explicitly saying 'existing'. The requirement of Id and SyncToken adds specificity, making the tool's purpose unmistakable.

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 implies this tool is for updating existing records, but it does not explicitly mention when to use it over alternatives (e.g., create_company_currency for new currencies, delete_company_currency for removal). It also doesn't state that fetching the currency first is required to obtain SyncToken, though the schema implies it. No direct guidance on alternatives or exclusions.

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