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

With no annotations, the description carries the full burden and does well: it discloses the ~30-second lifetime, that the release is audit-logged, and that the underlying seed is never exposed. It stops short of stating permission/identity requirements or what happens when the code has expired or the site is unknown, so it is strong but not exhaustive for a credential-adjacent tool.

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 short sentences, zero filler. Purpose and constraint come first, then the TTL/audit/no-seed disclosure, then the sibling routing hint — a well front-loaded ordering.

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 2-parameter tool with no annotations and no output schema, the description supplies the return shape (six digits), its validity window, and the security guarantee that the seed is not returned. The only real gap is the meaning/format of the required site parameter, which neither the schema nor the description explains.

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 only 50%: identity_id is documented in the schema (omit when the account has exactly one identity), but site has no description anywhere. The description mentions "site" only in passing and never says whether it is a domain, a saved-site label, or how matching works, so the undocumented parameter is not compensated for.

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 ("Return the current six-digit authenticator code") and names the constrained scope ("for a site") plus the audience condition ("agents whose browser runnerID cannot reach"). It explicitly separates itself from the sibling fill_code, so an agent can distinguish it without opening any 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?

Gives both the when-to-use condition (browser runnerID cannot reach) and the preferred alternative with its triggering condition ("Prefer fill_code when you have a cdp_url"). That is an explicit routing rule between two competing tools, which is exactly what usage guidance should do.

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