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

Annotations already declare readOnlyHint=true and openWorldHint=true, and the description is consistent with a safe read. Beyond that, it discloses meaningful domain behavior the annotations cannot: which days are excluded (weekends, public holidays, midsommarafton, julafton, nyarsafton) and what the return payload contains.

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 tightly packed sentences, front-loaded with the core operation and immediately followed by the mode variant and the return summary. No filler, though the parenthetical holiday list is dense enough that it slightly taxes readability.

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 no output schema, the description compensates by summarizing the return value (result date with weekday, ISO week, and holiday names for both dates). Combined with full parameter coverage and the mode explanation, an agent has everything needed to call and interpret this tool correctly.

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%, so the baseline is 3. The description adds real meaning beyond the enum labels by defining mode=work as 'counts only weekends and red days', clarifying how it differs from the default. The 'add' sign/max semantics are left to the schema, which already documents them.

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 (adds/subtracts) plus the exact resource (Swedish bank days) and the input it operates on (a date). The definition is unambiguous and, unlike every sibling tool (dns, email, iban, url, etc.), covers a distinct domain so there is no risk of confusion.

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 explains the two operating modes (default 'bank' vs mode=work) and what each counts, giving the agent clear context for when each applies. It does not give explicit when-not-to-use guidance, but no sibling tool offers an overlapping capability, so that omission is minor.

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