create_subscription

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It does reveal that the operation is 'Escopo write' (write scope) and that it is idempotent per (customer, offer), which are useful behavioral traits. However, it does not explain permissions, reversibility, response behavior, or error conditions. For a write tool with zero annotations, this is a moderate disclosure, more than just 'creates', but still lacking richer detail. A 3 is justified.

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 two concise sentences with no filler. It front-loads the primary purpose and then adds the key constraint of idempotency and write scope. Every word earns its place.

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 10 parameters, only 2 required, no output schema, and no annotations, this is a complex write operation. The description is brief and does not clarify important aspects like how to choose between Pix manual and migration flows, which parameters are essential (such as external_id and offer_slug), the role of current_period_end for migration, or any side effects. It leaves the agent to infer too much from the schema. A 2 is appropriate for this incompleteness.

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 schema has only 20% description coverage, with only 'phone' and 'current_period_end' having descriptions. The overall description mentions 'cliente' and 'oferta' in the idempotency note, but does not map them to specific parameter names (external_id, offer_slug). It provides no guidance on required fields, the meaning of collection_method, coupon_code, or activation. The description adds essentially no parameter semantics beyond the schema, failing to compensate for the low coverage. Thus a 1.

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 precisely what the tool does: 'Cria uma assinatura SEM cartão (Pix manual ou migração)'. It specifies the resource (assinatura/subscription) and the mode (without card, via Pix manual or migration), and distinguishes it from sibling tools like get_subscription, cancel_subscription, and change_plan. It is a specific verb+resource statement with clear scope.

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?

The description gives clear context: use this tool to create a subscription without a card, either via manual Pix or migration. It also mentions idempotency by (customer, offer), which implies when the tool can be safely re-invoked. However, it does not explicitly state when to use an alternative (e.g., card-based subscription creation), but that is not among the siblings. There are no exclusions or alternatives named, so a 4 is appropriate.

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