Describe sources

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

The annotations already mark it readOnly and openWorld; the description confirms a non-destructive read-and-check behavior. It adds value beyond the annotations by explaining that the tool lists per-source layers/fields and cross-checks layer references, and by clarifying accepted style inputs.

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 deliver the operation, the validation behavior, concrete use cases, and input forms without any filler. The main action and when-to-use guidance are front-loaded.

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 tool with no required parameters and no output schema, the description gives enough to invoke it correctly: what it inspects, what it validates, when to call it, and the three supported inputs. It leaves open the exact return structure, but the stated behavior ('lists' and 'checks') covers the essential expectations.

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?

The input schema already describes all three parameters at 100% coverage. The description's 'object, a URL or a file path' maps cleanly to style/url/path, but it doesn't state that exactly one should be provided or define precedence, so it adds little beyond the schema baseline.

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?

The description names a concrete operation—'Reads the metadata of every source'—and enumerates what it produces ('lists the source layers and fields') plus the validation it performs. This makes it easy to distinguish from siblings like describe_style_spec (spec-level) and validate_style (style-level), since the focus is squarely on sources and their data layers.

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?

It gives explicit triggers: use it 'before writing layers against data you do not know' and 'when a layer draws nothing.' It doesn't mention when not to use it or name alternatives, so it misses the top rung but provides solid contextual guidance.

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