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

Annotations already declare readOnly, idempotent, and open-world hints, so the safety profile is covered. The description adds useful context beyond annotations: it lists the content areas of the reference and states that no API key is required. This is appropriate for a no-parameter reference lookup.

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?

The description is two sentences with no filler. The first sentence front-loads what the tool returns, and the second delivers the usage instruction and auth note. Every clause earns its place.

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 no-parameter, no-output-schema reference tool, the description is complete: it states the content scope, the recommended invocation point, and auth requirements. Combined with the annotations, an agent has everything needed to select and call this tool correctly.

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 tool has zero parameters, so the description does not need to explain parameter semantics. The schema coverage is 100% vacuously; baseline 4 applies. No additional parameter meaning is required.

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 uses a specific verb ('Get') with a specific resource ('grammar reference for the OPC UA modeler YAML DSL') and enumerates the contents (file header, sections, naming conventions, examples, mistakes). This clearly distinguishes it from sibling tools like get_type_details or opcua_model_create, which address different resources.

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 explicitly instructs 'Call this FIRST before writing any YAML model by hand', which gives a clear condition for use. It also notes that it works without an API key, implying it is a low-friction first step. It does not name alternatives or explicit when-not-to-use cases, so it falls short of the full 5.

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