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

Annotations already cover the safety profile (readOnly, idempotent, openWorld, non-destructive), so the bar is lower. The description adds genuinely useful context beyond them: cost ('Free') and the exact return payload an agent can expect. It does not mention rate limits or auth, but for a free public read it adds value above what the structured fields provide.

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 dense sentence front-loads the cost/usage cue ('Free. Use when...') and then packs purpose, return fields, and both accepted input formats with no filler. Every clause carries information.

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?

There is no output schema, so the description carries the burden of describing return values – and it does so explicitly (title, date, in-force status, EUR-Lex link). Combined with the input-format examples and safety annotations, nothing needed to call the tool correctly 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 coverage is 100%, so baseline is 3, but the description supplies concrete input examples the schema only restates: a CELEX number (32016R0679) and free-text citations (Directive 2015/849). This clarifies that two different identifier formats are accepted, which is useful disambiguation.

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 (lookup) and resource (EU regulation/directive/decision) and enumerates exactly what is returned: official title, date, in-force status, EUR-Lex link. This cleanly distinguishes it from sibling checks like eu_company_check or eu_vat_check, which target different EU identifiers.

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 clear triggering condition ('use when the user cites an EU regulation, directive or decision and you need its official title, date, whether it is still in force, and the EUR-Lex link to cite'), which is strong context. It does not name an alternative tool or state when not to use it, but the sibling set has no overlapping citation-lookup tool, so this is near-sufficient.

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