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

Annotations only carry destructiveHint=false, which says almost nothing for an auth tool. The description compensates by disclosing the return artifact ('Returns a session token used for account and project management'), which is essential since there is no output schema. It still omits failure behavior (invalid credentials), token lifetime/expiry, and whether logging in invalidates existing sessions.

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 sentences, no filler, and front-loaded: purpose first, then the return value, then the alternative-route caveat. 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?

With no output schema, the description correctly supplies the return value and notes the token's downstream role. It stops short of documenting error/credential-failure behavior and token expiry, which an agent calling a login tool would benefit from.

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 100%, and both parameters are trivially self-documenting ('Email address', 'Password'), so the baseline 3 applies. The description adds no format, validation, or sourcing guidance beyond the schema.

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 (log in), the resource/credential mechanism (email and password), and the platform. It also names the sibling it is not (login_google), letting an agent distinguish it from login_google, login_direct, signup, and the oauth_* tools 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?

Explicitly routes Google sign-in to the 'login_google' tool, which is a clear when-to-use-elsewhere statement. However, other closely related siblings such as login_direct and oauth_google_configure are not addressed, so an agent in a Directus/SSO context still has to guess.

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