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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds the non-obvious behavioral fact that mcp_personal_url is a secret containing the key, which an agent needs before echoing output — useful context beyond the annotations, though it doesn't spell out the exposure risk explicitly.

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 sentences, zero waste: the return contents come first, then the usage cue. The field enumeration earns its place because there is no output schema to carry it.

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 no output schema, the description compensates by enumerating the returned fields (login, key prefix and scopes, cabinet_url, mcp_personal_url). An agent has everything needed to call it and interpret the result.

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?

Zero parameters, so the schema baseline is 4 and there is nothing for the description to clarify. It correctly adds none of its own parameter detail, which is the right choice.

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?

States a specific verb ('Returns') and precise resource ('the account behind the API key in use'), then names the concrete fields returned. It is unmistakable against siblings like get_balances or list_transactions, which return different resources.

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?

'Use it to check you are connected to the right account' gives a clear triggering context. It doesn't name an alternative or state when-not to use it, but with no comparable sibling (nothing else reads the current key's account) the omission is minor.

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