use_account

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

Annotations already declare non-read-only, idempotent, non-destructive, closed-world. The description adds value beyond them: the side effect of creating an account on first use, the stability guarantee across restarts ('same role maps to the same account'), and the session-exclusivity failure mode. It does not state auth/permission needs, but the disclosure beyond annotations is substantial.

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?

Four sentences, front-loaded with the core action, then the two modes, then the persistence and exclusivity guarantees. No filler, though the sentence count is slightly higher than strictly needed and the mode explanation overlaps the schema descriptions.

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?

No output schema exists, so the description usefully covers what the no-arg mode returns ('description and whether in use'). Combined with the dual-mode rules and the session-lock constraint, an agent has enough to call it correctly; only auth expectations and the retrieval-mode return shape for the login path are unstated.

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 the schema already documents both params, including the 'omit to only list roles' semantics for role. The description reinforces the mode switch but adds no new meaning about maxLength, the description param's audience, or formatting. Baseline 3 applies when the schema does the heavy lifting.

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+resource ('Selects this session's account (role)') and immediately clarifies the dual-mode behavior (no args = list roles; with role = log in). It is clear on its own, but it never disambiguates against the sibling list_accounts, which appears to also expose account/role listings.

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 the selection rule for each mode: omit role to list, supply role to log in and create if needed. It also states a real precondition ('A role used by another session cannot be selected'). No alternative sibling tool (e.g. list_accounts) is named as an explicit alternative, so it stays short of a 5.

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