system_login

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

Beyond the sparse annotations, the description discloses that the password is sent as a tool argument and may be logged verbatim by MCP clients. It also reveals where credentials are cached (`~/.docker/config.json`), how they are reused, and that `system_logout` clears them. No annotation contradiction exists.

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 front-loaded with purpose, followed by critical security guidance, then parameters and return values. Every sentence is informative and earns its place, and nothing is repeated from the annotations or schema in a way that bloats the text.

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 zero schema-level parameter descriptions and no output schema, the description is unusually complete: it explains safety, side effects, parameter defaults, and the exact return shape. Edge-case failure modes are not described, but enough context is present for correct selection and invocation.

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 schema provides 0% description coverage, so the description carries the full parameter burden. It explains every parameter: username, password-or-token, email, registry defaulting to Docker Hub, `reauth` force behavior, and the custom dockercfg path. This adds real meaning beyond the raw 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?

The description opens with a specific verb and resource: 'Authenticate with a Docker registry.' It also explains what the credentials unlock (`image_pull` / `image_push`) and names `system_logout` as the tool that clears them, which distinguishes it from the sibling set.

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 explicitly tells the agent when NOT to call this tool: prefer host-side `docker login` and avoid calling it from an agent loop. It also gives when it is needed, namely reaching private repositories through `image_pull` / `image_push`, and names the sibling that reverses the action (`system_logout`). This is strong usage guidance.

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