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

With no annotations, the description carries the full burden, and it does well: it discloses the returned fields (bank, amount, due date, check-digit results), flags a real domain caveat (ambiguity from the Febraban 2025 factor reset), and even states the cost ($0.005). It stops short of describing error behavior for malformed codes, but this is a stateless pure decode function whose safety profile is self-evident.

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 tightly packed sentences plus a price tag; the input formats come first, then return values, then the ambiguity caveat. Every clause carries information an agent would otherwise have to guess.

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?

There is no output schema, yet the description names the returned fields, so an agent knows what to expect back without one. The only gap is failure handling — what happens to a code that fails the check digit — which is minor for a simple decode utility.

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 single parameter is fully documented in the schema (100% coverage), so the baseline is 3, but the description adds digit-count semantics (47/48/44) that tell the agent exactly what a valid 'code' looks like, going beyond the schema's generic 'digitable line or barcode' phrasing.

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?

States a precise compound verb ('validate and decode') on a specific resource ('Brazilian boleto') and enumerates the exact accepted input shapes (47-digit cobranca, 48-digit arrecadacao, 44-digit barcode). The resource itself cleanly separates it from the sibling decode_pix.

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 accepted input forms imply when the tool applies, but the description never states when to use it versus alternatives (e.g., decode_pix for Pix keys, validate_identifier for other identifiers) or any prerequisites. Usage is only inferable from the tool's subject matter.

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