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

Annotations already declare readOnly, idempotent, openWorld, non-destructive, so the safety profile is covered. The description adds the meaningful workflow trait that no dataflow lookup is required, which is the key behavioral distinction an agent needs. It stops short of explaining failure behavior for unknown ids or that `limit` defaults to 100 and can truncate a large codelist.

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 sentences, front-loaded with purpose, followed by the when-to-use rule and two compact examples. Slightly redundant in that the example codelist id `CL_ECO` duplicates the schema example, but nothing pads the definition.

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?

With no output schema, the description correctly indicates the return shape ("code->label mapping"). It is nearly complete for a six-parameter read tool, with the one meaningful omission being that the default `limit` of 100 can truncate large codelists, which an agent calling it for a full mapping would want to know.

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% and every parameter, including enum values for `registry` and defaults for `limit`/`version`, is already documented in the schema. The description's examples show realistic `id`/`registry`/`filter` combinations but add no semantics beyond what the property descriptions provide, 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 ("Fetch one codelist's code->label mapping by id"), plus the scope qualifier "from any SDMX 2.1 registry, without needing a dataflow." This makes it clearly distinct from siblings sdmx_dataflow_structure and sdmx_find_dataflow, which are referenced by name.

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 states the triggering condition ("Use this when you already know a codelist id"), names where such an id can come from (sdmx_dataflow_structure's `codelist` field, dataset documentation), and provides concrete invocation examples. No inference about when to prefer this over the dataflow tools is required.

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