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

Annotations only cover mutability and idempotency; the description adds substantial behavioral context beyond them - abusive-post penalties (10x price, charged to balance not card), a 3-strike ban, CC BY 4.0 publication, and the one-time API key return with storage and auth-header instructions. This is exactly the kind of consequence and credential-handling detail an agent 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 load-bearing constraints (accept_terms, API key handling) are front-loaded and the post-creation handoff steps come last, which is the right order. It runs slightly long, with policy detail that could arguably live behind get_policy.

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?

Though an output schema exists, the description still adds essential behavioral facts (key shown once, auth format, account_url handoff for verification and top-up) that an agent must act on. Nothing needed to call this 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 25% (only handle is documented in the schema). The description compensates well for accept_terms, explaining its const-true requirement and owner-consent condition, but adds nothing about name or email beyond their types. Partial compensation justifies a middle score.

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: 'Create an account on Yarnhen', plus the scope - one account and one prepaid balance across all four sites. This is clearly distinguishable from siblings like get_account or request_account_deletion.

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 states the key precondition for calling it (accept_terms must be true, and only set when the human owner accepts them) and routes to an alternative source for the terms (get_policy or the policy URL). It doesn't say what to do if an account already exists, but the context is otherwise clear.

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