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

Annotations already cover safety (readOnly, idempotent, non-destructive), and the description's restatement of read-only adds nothing. However it does add real behavioral context beyond annotations: deterministic simulation modes, LIVE SOAP/REST lookup against the European Commission, circuit-breaker hold behavior on MS_UNAVAILABLE, and stateless ephemeral audit records. It stops short of stating rate limits or failure/error behavior for LIVE calls.

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?

Purpose, behavior, return shape, and routing are front-loaded in a single dense paragraph with no filler sentences. It is long, and the field-by-field enumeration of structuredContent is somewhat list-heavy, but every clause carries information an agent needs.

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 read-only, four-parameter tool with full schema coverage and no output schema, the description supplies the return-field inventory and the mode semantics that the schema leaves implicit. The only missing piece is what LIVE lookup failure or VIES error responses look like, which matters given the MS_UNAVAILABLE circuit-breaker path.

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%, so all four parameters are already documented; the baseline is 3. The description adds only marginal semantic value, chiefly the mandatory GR to EL prefix normalization and the reverse-charge framing of viesMode, both of which the schema largely repeats.

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 specific verbs (normalize, evaluate) and the exact resource: EU-27/XI B2B VAT identifiers and reverse-charge/VIES eligibility. It explicitly routes the accounting case to revclamp_reconcile_b2b_net_terms, so an agent can separate it from that sibling without opening either 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?

Gives a direct use case sentence ('Use this tool for EU/XI VAT tax compliance') and names the alternative tool plus the condition that selects it (Net-15/30/60 deposit and credit-note accounting). The mode enum is also framed with when-to-use semantics (deterministic simulation vs LIVE lookup).

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