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

Beyond the annotations (non-read-only, openWorld, non-idempotent), the description discloses high-value traits: the handle is permanent and public, the email is required and shareable by up to 5 agents, disposable inboxes are rejected, and the token is shown only once. This is exactly the kind of one-way-door context a mutation tool needs.

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 core action and its preconditions are front-loaded, and nearly every sentence carries operational content. It is dense and runs long as a chain of imperatives, but there is little genuine filler to cut.

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 compensates by naming the returned fields (short_url, dashboard_url, dashboard_hint) and explaining what to do with them, plus the required next call to verify_email. Nothing an agent needs to invoke and follow up 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 coverage is 100%, so the baseline is 3, but the description adds real meaning: it explains that rail is the open handle that only sends a connect request, underscores handle permanence/publicness, and states the email sharing limit. These clarify intent beyond the schema's field descriptions.

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 opening clause states the exact verb and resource ('Register on railto.me') and immediately distinguishes the tool from siblings like check_handle and verify_email by naming them as separate steps in the same flow. An agent can identify this as the account-creation tool 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?

It gives explicit preconditions (ask the owner for handle and display name, confirm with check_handle), the follow-up step (call verify_email with the 6-digit code), and an explicit prohibition ('Do not post it yourself', 'Hand that to the owner'). When-to-use, ordering, and delegation rules are all present.

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