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

Annotations already carry the safety profile (readOnly, idempotent, non-destructive, open world), so the bar is lower. The description still adds real value by disclosing the output content — two public lookup URLs from named sources plus court metadata — which matters since no output schema exists. Auth, rate limits, and invalid-ECLI behavior remain unstated.

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?

Two sentences, zero filler: the capability and its outputs come first, the format example second. Nothing is repeated from the title or schema, and 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?

For a one-parameter resolver with rich annotations and no output schema, the description covers what the tool returns and gives a format example, which is sufficient to invoke it correctly. Only edge-case behavior (invalid or non-Belgian ECLI) is left uncovered, a minor gap.

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?

With a single parameter and 100% schema coverage, the baseline is 3, and the schema already says 'A Belgian ECLI identifier.' The description goes beyond that by supplying a concrete canonical example (ECLI:BE:CASS:2020:ARR.20200101.1), which anchors the expected format.

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 ('Resolve'), a specific resource ('a Belgian ECLI'), and the resulting artifacts ('canonical public lookup URLs (EU e-Justice + Juportal) plus court metadata'). The 'Belgian' jurisdiction qualifier cleanly distinguishes it from nl_legal_lookup / nl_rechtspraak_lookup / eurlex_lookup siblings without ambiguity.

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?

Usage is implied by the resource: you call it when you hold a Belgian ECLI. However, there is no explicit statement of when to prefer it over the sibling lookups (eurlex_lookup, legal_lookup, nl_legal_lookup) nor what happens with non-Belgian ECLIs, so routing must be inferred.

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