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

Annotations only declare readOnly=false, idempotent=false, destructive=false, while the description adds genuinely new context: the 6-hour TTL, the required Authorization header format, and the row-scoping behavior (user sees only their own records). It stops short of saying whether repeated calls invalidate prior tokens or what the response body contains, which leaves a small gap for a credential-issuing call.

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, both front-loaded: the capability and its constraint come first, then the consumption instructions. Every clause carries information and nothing is padded.

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 still identifies what is returned (a 6-hour session token), how to present it, and which endpoint it unlocks. For a two-parameter tool of this complexity, an agent has everything needed to invoke it and use 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?

Schema description coverage is 100%, with api_key documenting the pro_/pub_ distinction and app_user_id pointing to create_app_user. The description adds no parameter-level meaning beyond that, so the baseline 3 applies.

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 ('Get a 6-hour session token for an app user') and immediately bounds it with 'without email', which separates it from the human login flow. An agent can tell exactly what this produces without opening the 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?

Explicitly names the condition that selects this tool (app user with no email) and the alternative for real users ('sign in with an emailed code via /api/app-users/login'). It also tells the agent what to do next with the token, so there is no ambiguity about sequencing.

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