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

Annotations already mark this as non-read-only and non-idempotent, and the description adds useful behavioral context: the password/otp invariant and the role requirement for shared-login edits. It also reveals that sharing can be toggled through this tool. The partial-update semantics are not disclosed, but the description does not contradict the annotations.

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?

The description is two sentences with no filler. The first sentence states the action and scope; the second packs in both a data invariant and a permission constraint. Every sentence earns its place.

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 an 8-parameter mutation with no output schema, the description is minimal but viable. It covers the core invariant and authorization requirement, yet leaves important gaps like what happens with omitted fields, what the response contains, and why userId is required. The annotations cover safety but not operational detail.

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 only 13%, so the description must add meaning to parameters. It clarifies the password/otp_secret invariant and the behavior around the 'shared' field, but leaves required userId, id, domain, username, and nullability semantics implicit. The most important constraints are covered, but not enough to fully compensate for the low schema coverage.

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 ('Update') and resource ('a login') with an id scope, making the basic operation clear. It is distinguishable from createCredential and deleteCredential, though it doesn't explicitly name them or clarify the 'credential'/'login' terminology.

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 provides actionable usage constraints: at least one of password or otp_secret must remain set, and editing team-shared logins or toggling sharing requires lead builder role. This helps an agent decide whether a requested update is valid or permissioned, though it does not explicitly contrast with sibling tools.

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