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

The description adds substantial context beyond readOnlyHint: the signing model ('Signed with your App/Secret key only, no user token yet'), the endpoint, and the response shape ({ AuthToken }). It stops short of disclosing failure behavior (e.g., invalid credentials or rate limits on repeated logins), which would be the remaining useful detail for a credential-consuming 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?

Three dense sentences, all front-loaded with the core exchange operation before the endpoint and bootstrapping advice. Every clause carries information the agent needs (auth inputs, endpoint, signing key, return value, one-time usage).

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 two-parameter credential-exchange tool with no output schema, the description covers inputs, auth context, endpoint, return value, and usage lifecycle. Nothing an agent needs to call it correctly 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?

Schema description coverage is 100%, so the schema already documents both parameters, making 3 the baseline. The description adds only marginal clarification by mapping password to the 'website login PIN/password' and labeling username as an account username, nothing about format or validation beyond that.

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 verb and resource ('Exchange a username + PIN/password for that user's authorization token') and pins down the exact underlying endpoint (POST /v1/user/login). It is unmistakably distinct from the other siblings, which are all broadcast/list/account operations.

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?

It gives explicit lifecycle guidance: 'Use this once to bootstrap; store the token in config thereafter,' which tells the agent both when to call it and when not to call it again. It does not name an alternative sibling for token reuse, but the once-only framing is clear enough that no inference is needed.

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