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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so the safety profile is covered. The description adds that the tool returns a legal form hint and the derived Swedish VAT number, which is useful behavioral context absent from structured data (no output schema). It stops short of describing error behavior or output shape in detail.

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?

One sentence, front-loaded with the verb and resource, and no wasted words. The parenthetical alternative and return description are integrated efficiently.

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 simple read-only validation with one parameter and no output schema, the description supplies the input alternative and the return contents. It is sufficient for correct invocation, though it could state invalid-input behavior or error format to be fully complete.

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 single parameter has an example ('556036-0793'). The description adds that the input may also be an SE...01 VAT number, going beyond the schema's example and clarifying accepted formats. This is meaningful additional semantics for the only parameter.

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 (Validate) and resource (Swedish organisationsnummer, with an SE...01 VAT number alternative). The resource is unambiguous and distinct from sibling validate_personnummer, so an agent can select it without opening the schema.

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 description does not say when to use this tool versus sibling validate_* tools, nor does it list prerequisites or exclusions. Usage is only implied by the resource name; no explicit routing guidance is provided.

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