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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so safety needs no restating. The description adds genuine domain context the annotations cannot: the legal basis of the calendar (Law 2429 plus Diyanet), the Monday–Friday-minus-holidays definition, and the 13:00 eve cutoff.

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?

Three sentences, each carrying distinct load: what it returns, what calendar it follows with its date range, and how business/half days are defined. Front-loaded with the core answer, no filler, no repetition of schema or annotations.

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?

Return values are covered by an output schema and safety by annotations, so the remaining burden is domain scoping, which the description handles well including the 2022–2035 limit. It stops short of saying what happens for out-of-range dates, a minor gap for a lookup tool.

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 100% and the three calendar enums are described there, so the baseline is 3. The description earns an extra point by supplying the underlying rule for the half_days parameter ('Eves ... are half days (holiday from 13:00)'), which tells the agent why the enum exists and what it changes.

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 and resource ('Tells whether a date is a business day in Türkiye') and additionally discloses the two extra facts returned: the holiday name and half-day status. This functionally separates it from list_holidays and count_business_days, though it never names those siblings explicitly.

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 is implied by the purpose rather than stated: nothing says 'use this to validate a single date' versus using count_business_days or add_business_days. The coverage window (2022-01-01 to 2035-12-31) is a useful boundary hint, but there are no explicit when/when-not rules or sibling routing.

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