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

The description adds significant behavioral context beyond the annotations (readOnlyHint=true): it explicitly states the tool is deterministic and auditable, explains the day-by-day month counting, and clarifies the effect of missing INPC parameters. No contradiction with annotations.

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 concise, consisting of three sentences that are front-loaded with the main purpose. Each sentence adds value: purpose first, then behavioral details, then a disclaimer. No redundant or extraneous text.

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?

The tool has 5 parameters with thorough schema descriptions and the description adds operational context. However, since there is no output schema, the description could have mentioned the return format (e.g., total amount, breakdown). Despite this minor gap, the description is fairly complete for a calculation tool with clear inputs.

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 input schema has 100% coverage with descriptions, but the tool description adds additional meaning: it explains the month-counting rule (cada fraccion = mes completo), specifies the optionality and impact of INPC parameters, and clarifies that the amount is in pesos. This enriches the semantic understanding beyond the schema alone.

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 clearly identifies the tool as calculating late payment surcharges for Mexican contributions, referencing specific legal articles (CFF Art. 17-A y 21). This specific verb+resource combination distinguishes it from sibling tools like fiscal_imss or fiscal_isr_retencion, which handle different fiscal calculations.

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 provides clear context: it's deterministic, auditable, and explains the month-counting method. It also states the condition about INPC parameters. However, it lacks explicit guidance on when to prefer this tool over siblings or when not to use it (e.g., if not in Mexico).

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