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

Beyond the annotations (readOnlyHint: false, idempotentHint: true, destructiveHint: false), the description discloses a key side effect: 'Stores the user session token in this MCP session and unlocks user-auth tools.' It also lists error codes (401/403, 404, 429) with rate-limit retry advice, which is valuable behavioral context that the annotations do not provide.

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 dense but efficient: three sentences cover the main purpose, session side effect, auth prerequisites, and error handling. It is front-loaded with the core action, and every sentence adds essential information with no fluff or redundancy.

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 login tool, the description covers all necessary operational aspects: the credentials to use, the required auth context, the resulting session behavior, and error handling. There is no output schema, but because the session token is stored internally, a return value description is unnecessary. The context signals and sibling tools further make the place of this tool clear.

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 has 100% description coverage for all five parameters, including details like format, purpose, and defaults. The tool description only repeats 'email + password' and adds no extra meaning beyond what the schema already documents. This meets the baseline of 3 as the schema carries the parameter burden.

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 and resource: 'Authenticate as an existing Ethora user with email + password.' This clearly distinguishes it from sibling tools like ethora-user-register and the auth-mode selectors, making the tool's role unambiguous.

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 specifies the prerequisite 'user-auth mode (`ethora-auth-use-user` first) and a configured `appJwt`', which tells the agent when this tool can be used. It also notes that it 'unlocks user-auth tools', implicitly guiding the agent to choose login when those tools need to be accessed. It does not explicitly name alternatives for app or B2B auth, but the user vs. app distinction is clear.

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