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

Beyond the readOnly/idempotent annotations it discloses auth requirements (aa_ key or MCP OAuth token), the full status vocabulary and the fact there is no 'done' status, null return for a missing session, and that user_id/email are null until completion. This is substantive behavioral context the annotations cannot convey.

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?

Purpose and sequencing are front-loaded, and the enumeration of return fields is justified by the absence of an output schema. It is dense and runs long, but nearly every clause carries information the agent needs; only the field list slightly overlaps schema-level concerns.

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 carries the full burden of describing return values and does so: it lists the returned fields, enumerates status values, explains null semantics and the missing-session case, and names the follow-up tool for webhook failures. Nothing needed to call it correctly is missing.

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 there is one parameter, so the schema already documents session_id. The description restates its provenance ('passing that call's sessionId') but adds no syntax or format detail beyond the schema, so the baseline applies.

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 and resource ('Poll one login-link session until the human finishes') and immediately scopes it against siblings by tying it to create_login_link and retry_login_webhook. An agent can distinguish it from the other login tools without opening a 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?

Explicit sequencing ('Use this after create_login_link, passing that call's sessionId'), plus an exclusion routing to retry_login_webhook when webhook delivery failed and a clarification that it does not send a new notification. When-to-use and when-to-use-something-else are both covered.

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