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

Goes well beyond the annotations by disclosing the 409-on-second-call behavior, the token requirement, and that no current password is needed the first time. One minor tension: idempotentHint=true while the description says a repeat call errors with 409, which the text never reconciles (state is unchanged, but the call is not a silent no-op).

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?

Dense but well front-loaded: the account scope and the one-time nature land in the first two sentences. Slightly over-specified at the tail, where the 409 error is stated twice ('returns 409' and again 'Typical error: 409 password already set'), which is mild redundancy rather than 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?

With annotations covering the safety profile, a fully described single parameter, and no output schema to explain, the description supplies everything needed: auth requirement, first-call-only semantics, password constraints, and the error-to-action mapping. Nothing an agent needs to invoke 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 coverage is 100% and the single param is already fully documented ('at least 8 characters with letters and numbers'). The description adds the useful clarification that there is no current-password parameter on the first call, but otherwise mirrors the schema. Baseline 3 is appropriate 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 and resource with tight scope: 'Set a password for THIS account (the one your bearer token belongs to).' It distinguishes itself from nearby siblings (register_account, login) by explaining the account's default no-password state and the credential model, so an agent can place it 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?

Explicit when-to-use ('Call this ONCE to enable email+password login as a recovery method'), when-not ('If a password was already set, this returns 409'), and the alternative ('use change-password instead'). This is the exact when/when-not/alternative structure a routing agent needs.

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