list_available_fields

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

With no annotations, the description carries the full burden and does so well: it discloses that 'fit' returns an empty list, that an unknown domain silently returns no fields rather than erroring, and that narrowing by domain produces a much smaller result. These are non-obvious edge-case behaviors an agent would otherwise have to discover by trial.

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?

Front-loaded with purpose and trigger, then parameter behavior, then return shape — a sensible order. It is dense and slightly long, but every clause carries operational information (edge cases, units, _series naming convention), so little 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?

There is no output schema and no annotations, yet the description fully documents the return payload (domains, metadata_kinds, fields, units) and the _series naming convention. Nothing needed to call or interpret this tool 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 0% — the domain parameter has no description or enum in the schema — so the description must compensate, and it does: omit domain for the full overview, pass 'health' or 'context' to narrow, and the special-case 'fit' returns empty. This is richer than the schema by a wide margin.

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 ('List the queryable fields') plus the grouping dimension ('by domain and source'). It explicitly differentiates from siblings by noting that query_raw's fields are excluded and named elsewhere, and it names query_health and query_context as the consumers of the output.

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 an explicit trigger ('Call this first when the exact field name for query_health or query_context is unknown') and names the sibling it does not cover (query_raw). No ambiguity about when to reach for this tool versus the query tools.

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