Logs user into the system.

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

The description directly contradicts the annotations: readOnlyHint is true, but 'Log into the system' implies a session-creating side effect. No behavioral details (e.g., token return, session expiry) are disclosed beyond the misleading annotation.

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 extremely brief and does not waste words, but it is under-specified to the point of adding nothing beyond the title. It is concise but not meaningfully structured or informative.

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?

Given the absence of an output schema and the simple parameter set, the description should still explain expected behavior or return value. It fails to mention success/failure outcomes, session details, or the effect of invalid credentials, making it incomplete for a login action.

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?

The input schema already provides full descriptions for both username and password (100% coverage). The description adds no additional parameter semantics, so it meets the baseline for schema-documented parameters.

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 'Log into the system' clearly states the action and resource, distinguishing it from siblings like get_user_by_name or update_user. However, it is virtually identical to the name and title, adding no new specificity, so it does not earn a 5.

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?

The description offers no guidance on when to use this tool versus alternatives (e.g., get_user_by_name for fetching user info), nor any prerequisites like the user existing or session handling. It is entirely absent of usage context.

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