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

Adds substantial context beyond the annotations: token lifetimes (10h access, 30d refresh), the fact that the response is delivered only once and must be persisted immediately, and the fallback path when renewal fails. This is exactly the operational knowledge the readOnlyHint/idempotentHint flags cannot convey.

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?

Front-loaded with the core exchange and token lifetimes, with error branches in descending priority. Slightly redundant: the persist-both-tokens and use-refresh_access_token advice is repeated near the end, and the trailing EN keyword list is filler.

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?

There is no output schema, and the description compensates by naming exactly what is returned (access_token + refresh_token, once only), plus lifetime and persistence requirements. Nothing an agent needs to call this 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 coverage is 100% and already maps client_id to username/email and client_secret to password/secret, so the description adds little on these two fields. It does clarify the OAuth framing (grant_type=refresh_token for the sibling), but that concerns renewal, not this tool's own parameters.

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 concrete verb+resource: exchange client_id/client_secret for access_token + refresh_token. It explicitly distinguishes itself from register (account creation) and refresh_access_token (renewal), so an agent can route correctly without opening other schemas.

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?

Gives explicit when-to-use (once at the start), when-not (do NOT log in again; use refresh_access_token, which needs no password), the prerequisite (register first if no account), and the out-of-scope case (forgotten password is done by a human via the web UI, no tool exists).

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