generate_mac_emv_pin_change

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

With no annotations, the description carries the full behavioral burden. It clearly discloses that three separate keys are required, assigns roles to P0/E2/E1, and calls out that ISO_FORMAT_4 is unsupported. It does not mention the return value or failure modes, but the key and format constraints are well covered.

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 well structured with a clear call-to-action, important warning, key-type summary, and argument list. There is some redundancy between the 'Required key types' block and the Args section, but for a high-stakes cryptographic operation the repetition reinforces critical constraints without becoming rambling.

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?

Given the complexity—7 required parameters, a nested object, no annotations, and no output schema—this description covers the essential decision points: when to call it, what prerequisites exist, and what each parameter means. The only notable gap is that it does not explicitly describe what the operation returns, which would be useful without 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?

Schema coverage is 0%, and the description compensates by explaining all seven parameters, including ARN/alias expectations and hex encoding. The main weakness is derivation_method_attributes, which is only described as 'Visa, Mastercard, etc.' rather than giving a precise structure or accepted values.

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 operation: generating an EMV PIN change MAC for issuer scripts, CHANGE REFERENCE DATA (INS=24), or offline PIN change MAC assembly. It also distinguishes itself from single-key EMV MAC helpers, making the tool's purpose and scope unambiguous.

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?

Explicitly instructs when to use the tool: 'Call this before implementing any EMV PIN change flow.' It also states when it is not sufficient—single-key EMV MAC helpers (E2 only) cannot replicate this—and explains that all three key types must be provisioned in APC separately.

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