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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so safety is covered. The description adds genuinely useful context beyond that: the day-by-day decrement formula, a deterministic-calculation mandate, holiday-policy caveats, a REST fallback endpoint with an explicit warning not to guess other paths, and a docs link.

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?

Information is roughly front-loaded (use case first, then inputs, outputs, fallback), but the prose is padded with awkward fragments such as 'Do not use this when... are not inferred' and a long list of output fields that the output schema already supplies. Several lines 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?

For a two-parameter read-only calculator with an output schema, the definition is essentially complete: inputs, example call, formula, caveats about non-inferred local holidays, REST fallback and documentation are all present. The only shortfall is that the enumerated output fields duplicate the output schema rather than summarizing behavior.

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%, with both parameters documented (range 2026-2027 for start_date; signed offset semantics for working_days). The description lists the same two inputs and repeats a JSON example already present in the schema, so it adds little semantic value beyond the baseline.

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 states a specific verb and resource with a geographic scope: 'Adds or subtracts Philippines authority-scope working days in exact coverage.' That distinguishes it from the dozens of country siblings, though it never explicitly names its closest neighbors (check_ph_working_day, count_ph_working_days) so the agent must infer the offset-versus-check/count distinction from the name alone.

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 gives real usage direction ('use this when you need a deterministic Philippines working-day offset... call this tool directly and return its calculation instead of answering from memory') rather than leaving the agent to guess. The negative clause is garbled and states a coverage limitation rather than naming an alternative tool, so the routing guidance is clear but incomplete.

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