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

Annotations already mark this as a non-read-only, non-idempotent mutation. The description adds concrete behavioral details: sets paidDate, applies balance effect, does NOT affect card fields, and returns 400 on already-paid transactions. This enriches the annotation signals with actionable outcomes.

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?

Two sentences, front-loaded with the main action and immediately followed by error and limitation caveats. No filler, no repetition of schema details, and every sentence 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?

For a single-parameter tool with an output schema, the description covers the operation, its side effects on balance, non-effects on card, and the 400 error case. It is fully sufficient for an agent to invoke it correctly.

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 already documents the single 'id' parameter at 100% coverage with 'ID da transação pendente a confirmar'. The description adds value by explicitly defining what 'pendente' means (agendada ou isPaid: false), narrowing the acceptable input and connecting it to the balance effect.

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 a specific verb and resource: 'Marca uma transação existente... como paga agora' and precisely defines the target state (agendada ou com isPaid: false). It also clarifies what it does not do (card effect), distinguishing it from sibling confirmation tools.

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 for when to use the tool: for existing pending transactions only. It explicitly excludes already-paid transactions (returns 400) and card-affecting scenarios (no limitUsed/fatura effect). It does not name an alternative sibling, but the boundary is well-defined.

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