validate_invoice_sg

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

With no annotations, the description carries the full burden and meets it: it discloses the dependency on the optional xslt2 extra, that a missing install returns level="unavailable", and that results carry a scope field and an EN16931-BASE-UNAVAILABLE warning. Failure modes and known limitations are surfaced before the agent 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?

The scoping is reasonably front-loaded, but the second paragraph leaks implementation detail unhelpful to an agent: a reference to validators/schematron.py's module docstring and the internal ticket [CORE-EN16931-BASE-SG-CROSSWALK-1]. Those sentences consume space without changing invocation behavior.

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?

An output schema exists, so return values need not be exhaustively explained, and the description still usefully names key result fields (scope, level, the warning code). For a one-parameter validation tool the coverage is adequate; only the alternative-tool routing for the uncovered rulesets is missing.

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% for the single xml_content parameter, whose schema text already specifies 'UBL 2.1 Invoice or CreditNote XML content to validate.' The description restates UBL 2.1 invoice XML but adds no format, encoding, or size guidance beyond the schema, so the baseline 3 applies.

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 a UBL 2.1 XML invoice against IRAS's C5 acceptance-layer Schematron — and immediately scopes what that means (IRAS's own acceptance layer, e.g. missing buyer/seller UEN). This is distinguishable from the sibling generate_invoice_sg and the various codelist/lookup tools.

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?

Explicitly defines when this tool applies (IRAS acceptance-layer checks) and, more usefully, when it does not: the CEN EN16931 base ruleset, PINT-SG overlay, and SG Peppol BIS Billing 3.0 are NOT checked. That negative scoping is strong routing guidance, though it never names an alternative tool for the unchecked rulesets.

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