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

Annotations already cover readOnly/idempotent/non-destructive, so the bar is lower. The description adds real context beyond that: the exact computation ('for each included date: working_days += status.is_working_day'), the authority-scope limitation, and an explicit REST fallback endpoint with a warning not to guess other /api/* paths.

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?

It is front-loaded with a use case and labeled sections, but it is heavily over-stuffed: example user requests, a full JSON example, a low-value pseudocode formula, and a REST fallback all compete for attention, and the malformed 'Do not use this when...' sentence is confusing. Several sentences do not earn their place.

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?

With an output schema present, the enumerated outputs are redundant, but the description still covers scope, inputs, edge limitations, and a fallback path. For a single-purpose counting tool with full annotation and schema coverage, it is essentially complete, with only the broken exclusion sentence detracting.

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%, so the schema already documents all four parameters (including defaults for the include_* booleans). The description merely restates the inputs and supplies a complete JSON example, adding no semantic detail beyond the schema. 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?

States a specific verb+resource: 'Counts authority-scope working and non-working dates in a range' for the Philippines. That is clear and distinguishes it from generic calculators, but it never distinguishes itself from the very similar siblings add_ph_working_days or check_ph_working_day, which an agent could easily confuse.

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?

'Use this when you need an auditable Philippines working-day count' and 'call this tool directly... instead of answering the formula from memory' give a usage context. However, the 'Do not use this when...' sentence is grammatically broken and describes scope limitations (local-government holidays, employer schedules, 2027 Eid) rather than naming an alternative tool, so the sibling-routing guidance is implied at best.

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