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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the safety profile is covered. The description adds real behavioral substance beyond that: it discloses the actual validation rule (Luhn check digit) and the nuance that the length digit is optional, which tells the agent what inputs will pass. It still omits how failure is signalled (boolean vs error), so it falls short of a 5.

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?

A single sentence that front-loads the verb and resource, then parenthetically supplies the two details that matter (Luhn, optional length digit). No filler or restatement of the name.

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 one-parameter validator with no output schema, the description should say what a call yields (valid/invalid boolean, error vs false) and any input-format constraints. It covers the validation rule well but leaves the return semantics entirely unspecified, which is a real gap given the absence of an output schema.

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 1 parameter and 100% schema description coverage, the schema already documents 'value' as 'OCR digits'. The description adds only the domain framing (Swedish OCR payment reference) and does not specify accepted format or expected length beyond the optional-length-digit note, so it meets the baseline without exceeding it.

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 specific verb (validate) and a specific resource (Swedish OCR payment reference), and names the algorithm (Luhn check digit, optional length digit). This clearly separates it from the sibling validators (validate_bankgiro, validate_iban, validate_personnummer, validate_plusgiro) without needing to open any schema.

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 domain-specific name and the algorithm note imply when this tool applies (validating a Swedish OCR reference), but there is no explicit statement of when to use it versus generate_ocr or the other validate_* siblings, and no preconditions are given. Usage is inferable rather than stated.

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