auth_login

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

Annotations are sparse (readOnlyHint=false, destructiveHint=false) and do not describe the flow, so the description carries the burden. It discloses that the tool returns a verification URL/code, that the server later receives credentials, and that API calls become linked to the user's account. It does not mention whether the tool blocks until browser completion, but the overall auth flow is reasonably transparent.

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 three sentences, front-loaded with the primary purpose, followed by return behavior and usage condition. Every sentence contributes useful information; the 'free tier, no credit card needed' aside is brief and relevant for adoption. No redundancy or fluff.

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 no-parameter tool with no output schema, the description provides the essential invocation details: what it does, when it is needed, and what it returns. A minor gap is not referencing auth_status as the follow-up to check completion, but the description sufficiently covers the immediate device-authorization flow.

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 tool has zero parameters, so the baseline is 4. The description adds meaning by explaining what the tool returns (verification URL and code) even though no output schema exists. There are no hidden parameters to explain, and the schema is complete with no additional properties.

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 starts with a specific verb and resource: 'Start the device authorization flow to connect this MCP server to your OpenEphemeris account.' It clearly differentiates from siblings like auth_status and auth_logout by describing the login initiation action. The free-tier note adds clarifying context without ambiguity.

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 states the precondition: 'Only needed if no OPENEPHEMERIS_API_KEY env var is set and no cached credentials exist.' This provides a clear when-to-use condition. However, it does not name alternatives such as auth_status or auth_logout, so it misses the explicit exclusion that would earn a 5.

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