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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the agent knows it's a safe, non-mutating operation. The description adds valuable context: it costs nothing, renders nothing, and returns specific error details (field path, expected type, received value, accepted value). This goes beyond the annotations and helps the agent understand the tool's behavior.

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 compact and front-loaded. The first sentence states the core function and output. The second sentence adds cost/behavior context. The third gives concrete usage guidance. No wasted words.

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 validation tool with readOnlyHint and openWorldHint annotations, the description is quite complete. It explains the return value (errors with field path, expected type, received value, accepted value), the cost (nothing), and the usage context. It doesn't describe the exact output format, but since there's no output schema and the description already lists the error components, this is a minor gap.

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 the schema already documents both parameters. The description adds meaningful context for the template parameter: how to pin versions (invoice@3) and the warning that new versions change output and cache key. It also clarifies that data is checked against the template's JSON Schema and nothing else. This adds value beyond the schema.

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's function: dry-run a data payload against a template's JSON Schema and return the exact errors a render would raise. It specifies the resource (template's JSON Schema) and the verb (validate/dry-run), and distinguishes it from the render tool by emphasizing it costs nothing and renders nothing.

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 says when to use it: before a batch, or whenever assembling a payload from an untrusted source. It also implies when not to use it (when you want an actual render) by stating it renders nothing. This is clear usage guidance.

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