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

Annotations already declare readOnly/idempotent/non-destructive/openWorld=false, and the description adds genuinely useful behavior beyond that: the coverage window (2026-2027), the exact formula used, deterministic output, named dataset_version/sources, and a REST fallback endpoint. This is meaningful disclosure beyond the structured hints.

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 definition is well segmented with clear headings (use/when-not/what it computes/inputs/outputs/formula/fallback/doc) and front-loads the decision criteria. It loses a little to redundancy: the full outputs list duplicates the existing output schema and the JSON example duplicates the schema example, and the typo in the first sentence is noise.

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 single-parameter, read-only calculation tool with an output schema, the description supplies the coverage boundary (2026-2027 only), scope exclusions, the formula, and a REST fallback, so an agent has enough to call it correctly. The redundant output enumeration is unnecessary given the output schema but does not leave gaps.

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 description coverage is 100% and the single 'date' parameter is already documented as a Gregorian date in the schema. The description only restates 'Inputs: date (date)' plus a JSON example, adding no format or constraint meaning beyond the schema, so the baseline 3 applies.

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 gives a clear verb+resource ('checks a date against the Saturday-Sunday weekend baseline and exact 2026-2027 authority events') and the opening sentence names the deterministic calculation intent. However the opening line has a duplicated word ('Mexico Mexico') and, despite a large sibling set (add_mx_working_days, count_mx_working_days, other check_*_working_day tools), it never explicitly says how this differs from the MX count/add variants.

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 provides an explicit 'Use this when' directive (deterministic result, return the calculation instead of recalling from memory) and an explicit 'Do not use this when' clause with scope exclusions (sector, state, employer, school and bank calendars out of scope). The exclusion sentence is convoluted and never names the sibling alternatives, so the routing guidance is present but imperfect.

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