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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds two things beyond that: the agency-key authentication requirement and the fact that the payload includes nested profiles, which is useful behavioral context for a single-account read.

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?

Two telegraphic clauses with the auth constraint and the resource scope front-loaded; nothing is wasted. The fragment style ('Agency key only') is terse but readable and appropriately sized for a one-parameter tool.

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 single-parameter read with annotations covering safety and no output schema, the description supplies the essential facts: what is returned (one account plus its profiles) and the credential requirement. Slightly more detail on the returned profile structure would make it fully self-contained.

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% for the single account_id parameter, so the schema already documents it. The phrase 'by id' adds no syntax, format, or constraint detail beyond what the schema's integer description provides, making baseline 3 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 names a specific verb and resource ('one account by id') and adds response scope ('with its profiles'), which distinguishes it from list_accounts and from get_profile/get_user. It stops short of explicitly naming the sibling alternatives, so it is clear but not maximally differentiating.

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?

'Agency key only' is a real precondition that tells the agent when this call is viable and implies a different path is needed with non-agency credentials. No explicit when-not statement or named alternative is given, but the auth constraint provides usable context.

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