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

Annotations already declare readOnly, idempotent, non-destructive and openWorld. Beyond that, the description adds genuine behavioral context: 'no call to Mureka' signals this is a local metadata lookup against the useapi.net token, not a live upstream fetch, and it discloses the failure surface (session health 'or the sign-in error'). It stops short of describing pagination or ordering.

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?

Three compact sentences, front-loaded with the purpose and return contents, then the routing guidance, then the HTTP endpoint. Every clause carries information — no filler or restatement of the title.

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 naming the returned fields (account id, sign-in mode, session health / sign-in error) and by flagging that the account id is the key other tools consume. Nothing needed to select or call this zero-param read is missing.

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 tool takes zero parameters, so the baseline is 4 and there is nothing for the description to disambiguate. It correctly adds no parameter discussion, keeping focus on the account-id discovery role.

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 and resource ('List every Mureka account added to this useapi.net API token') and immediately enumerates the returned fields (account id, sign-in mode, session health / sign-in error). It also names the two closest siblings it must be distinguished from (mureka_get_account, mureka_get_profile), so an agent can tell it apart without opening any schema.

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?

'Start here to find the account id other tools take' is an explicit routing instruction, and the alternative tools are named with the exact condition that selects them (session expiry → mureka_get_account; plan and Gold → mureka_get_profile). Both when-to-use and when-to-use-something-else are covered.

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