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

With no annotations provided, the description carries the full burden. It transparently discloses that the api_key is the only credential, that there is no password/email verification/browser step, and the exact authentication requirement ('must be passed in the Authorization header'). It also warns about MCP session reconfiguration, adding valuable behavioral context beyond what the schema or annotations would show.

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 longer than typical but every sentence adds value. It is front-loaded with purpose, then return value, then critical auth/credential details, then usage timing, then session-context workarounds. No redundant or filler content exists, though it could be slightly tightened without losing meaning.

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?

Despite having no output schema, the description explains the return value (api_key), its role as the only credential, the required auth header usage, and a specific same-session alternative. For a tool with four parameters and no output schema, this description provides complete operational context and preempts likely agent mistakes (e.g., not persisting the api_key).

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%, but the description adds meaningful extra semantics beyond the schema. The username parameter gets detailed auto-assignment behavior ('Heroku-style three-word handle like 'brave-amber-tiger'') and explicit guidance to prefer omitting it. The email parameter is contextualized as optional and not verified. This goes beyond the baseline for a high-coverage schema.

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 states a specific action ('Create a new bookstore4agents account'), the resource ('bookstore4agents account'), and the purpose ('so this agent can purchase, comment, and publish'). It distinguishes from siblings like rotate_api_key by explicitly noting the returned api_key is 'the only credential' and that no email verification or browser step is involved.

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 gives explicit when-to-use guidance: 'Call this when an agent has no credentials yet, or when the user explicitly asks for a new account.' It also provides critical context about session reconfiguration and a specific alternative path for this same session (passing the api_key to purchase_book), which clarifies tool selection and usage.

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