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

With no annotations, the description carries the full burden; it does disclose the specific checks performed (length, structure, mod-97) and the billing cost of 1 credit, which are genuinely useful behavioral facts. However it says nothing about what is returned, what happens for a malformed or invalid IBAN, or whether failures raise errors versus a validity flag — significant omissions for a validation tool with no output schema.

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?

A single front-loaded sentence conveys both modes, the checks performed, and the split-out behavior, with the cost tacked on compactly in parentheses. No sentence is wasted and the mode distinction is signposted by the "or".

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 3-parameter tool with no annotations and no output schema, the description should explain the return shape (valid/invalid plus parsed sort code and account) and the input-combination rule. It covers the input side and cost but leaves the output contract entirely unspecified, so an agent cannot anticipate the response.

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 nominally 100%, but every parameter is described only as "string", so the schema conveys no meaning; the description compensates partially by mapping sortCode/accountNumber to the UK format-check mode and iban to full validation. It still gives no format expectations (country prefix, length, digit-only sort code) that would prevent malformed calls, so this sits at the baseline rather than above it.

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 ("Validate an IBAN") and enumerates exactly what is checked — length, structure, mod-97 check digits — plus the secondary extraction mode and the alternate UK sort code/account mode. No sibling in the list does IBAN or sort code validation, so an agent can place it unambiguously.

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?

The "or" construction makes clear there are two operating modes and which inputs belong to each, giving contextual guidance without explicit exclusions. It stops short of stating the crucial rule that an agent must supply either iban OR sortCode+accountNumber (the schema marks zero required params), leaving the mutual-exclusivity condition implicit.

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