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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds that the output is a canonical URL, which is useful, but says nothing about failure modes for unknown codes/articles or upstream dependency on Justel.

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?

Three tight sentences with the action front-loaded, followed by the input contract and an example. Slightly list-heavy with the code enumeration, but nothing is wasted.

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 two-parameter read-only lookup with no output schema, the description is largely sufficient: it covers what the tool does and what it returns at a high level. It omits only edge-case behavior (invalid/unknown reference handling) and whether multiple matches are possible.

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 goes beyond the schema by enumerating a wider set of accepted codes (WBTW, WBE, Sw, Ger.W) and giving a concrete worked example (code=BW, article=4.71), clarifying the expected format of the optional article value.

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: 'Resolve a Belgian legislation reference to its canonical Justel URL'. The mention of Belgian/Justel distinguishes it from nl_legal_lookup and eurlex_lookup by jurisdiction, but it never explicitly names or contrasts a sibling tool.

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 implies usage ('Give the code ... and optionally the article number') but gives no when-to-use guidance, no exclusions, and no routing advice versus legal_search, legal_read, or nl_legal_lookup. The agent must infer that this is for canonical URL resolution while legal_read fetches content.

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