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

Annotations already declare readOnlyHint=true and destructiveHint=false, indicating no side effects. The description adds important context that it runs in an isolated environment and returns merged state without registration. It also mentions a throwaway runtime, which is consistent with read-only behavior. The description adds clarity on the isolation guarantee, which is a valuable extension beyond the annotations.

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 concise and front-loads the core purpose. It uses two effective sentences: the first covers the operation and outcome, the second states the intended use case. It is information-dense with zero filler, and the key differentiator (isolation) is prominent.

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?

The tool is complex with nested objects and rich schema, but the output schema exists, so return format is handled. The description covers the purpose, isolation, and intended use. It could mention the return value's shape or any error conditions, but given the annotation safety profile, this is sufficient for a correct invocation.

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 description coverage is 100%, so baseline is 3. The description adds context that mutations are applied within the dry run, reinforcing the isolation. But it does not explain the structure or constraints beyond what the schema already provides, so it meets the baseline without surpassing it.

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 clearly states the tool compiles a ModelSpec in an isolated runtime, applies optional mutations, and returns merged state without registration. It distinguishes itself from other tools by emphasizing the dry-run nature and preview capability, which is essential for correct selection.

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?

The description explicitly states 'Use this to preview the full reactive cascade of a draft spec,' which gives clear context for when to use it. It implies not to use it for final registration or when live registry effects are needed, but it does not explicitly name alternatives or exclusion criteria. Given the many siblings, this is adequate guidance.

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