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

The description adds substantial behavioral context beyond the annotations: the exact charge ($0.10/30 days), the 402-without-payment path, and the auth scope (X-Guest-Token guest vs. HTTP-only account session). However, it asserts repeated calls are effectively idempotent ('sem risco de pagar duas vezes'), which conflicts with idempotentHint=false.

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?

It is front-loaded with the price and purpose, and every clause carries operational meaning (cost, status codes, identity, storage). It is somewhat dense and repeats 'quem fala no chat' twice, costing a little crispness.

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 0-parameter tool with no output schema and sparse annotations, the description covers pricing, charge/idempotency behavior, status codes, identity scope, and where the purchase is recorded ('direito'). Only the success response body shape is left unstated, which is acceptable given no output schema exists.

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?

With 0 declared parameters, the baseline is 4. The description still adds meaning by identifying the implicit identity input, the X-Guest-Token header (recognized by the WebSocket 'hello') or the account session, which is not in the schema.

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 names a specific resource and scope ('Passe mensal do chat ($0.10 / 30 dias)') and the HTTP payment semantics (402 vs 200) make it clear this is a paid-pass acquisition endpoint. The verb itself is implicit rather than stated, but the resource is unambiguous and clearly separable from siblings like chat_send and chat_history.

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 tells the agent when it can be called ('dá para chamar antes de escrever, sem risco de pagar duas vezes') and describes the no-guest fallback path via the account session. It gives real context for invocation, though it never names a sibling alternative or states exclusions explicitly.

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