generate_mac

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

With no annotations, the description carries full behavioral burden and meets it: it discloses that CMAC always returns the full 16-byte MAC regardless of mac_length, that BIDIRECTIONAL DUKPT is only valid for AES and causes ValidationException with TDES, and that DUKPT key variants have direction rules. It also shows supported algorithms through generation_attributes examples. This is far beyond a minimal description.

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 long but densely organized: opening usage statement, key-type summary, generation_attributes examples, DUKPT rules, CMAC caveat, and an Args block. Every section adds operational information an agent cannot infer from the bare schema. The most important usage context is front-loaded before the technical details.

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 four parameters, nested objects, zero schema coverage, and no output schema, this description covers algorithm selection, key constraints, DUKPT derivation variants, MAC length semantics, and an important truncation edge case. It even routes to verify_mac for the associated verification workaround. There is no obvious missing information needed to call the tool 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?

Schema coverage is 0%, so the description must explain every parameter, and it does: key_identifier receives an ARN/alias plus valid key types, message_data is hex-encoded, generation_attributes gets algorithm-specific JSON examples, and mac_length is explicitly defined in nibbles rather than bytes with 8/16 examples. This fully compensates for the empty schema descriptions.

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 opens with a specific call-to-action: generating or validating MACs for ISO 8583 transactions, EMV issuer scripts, and payment message authentication. It lists concrete key types and ISO 8583 fields (64/128), and its closing note references verify_mac, helping an agent distinguish generation from verification. This is more specific than the bare tool name and clearly differentiates from siblings like verify_mac.

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?

It explicitly says 'Call this when implementing or validating MAC generation...' and even names a secondary use ('verify which MAC algorithm a given M-key type supports'). It provides key-type preferences and points to verify_mac for truncated-CMAC validation scenarios. It stops short of explicit when-not-to-use statements for every sibling, but the targeted context is strong.

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