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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the description does not need to repeat that. The description adds that it is 'local/runtime-backed', which is useful context beyond the annotations. However, it doesn't clarify side effects like whether execution produces logs or side effects beyond the call, or what happens on errors. Given annotations cover the safety profile, a 3 is appropriate.

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 a single concise sentence with no fluff. It front-loads the core purpose (execute function) and then specifies the input format. It avoids unnecessary detail, making it efficient. Only minor addition could be a mention of return behavior, but it's not critical.

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 full schema coverage and no output schema, the description provides enough for an agent to make the call: module and function names, args format, and the local-runtime boundary. It doesn't explain return values, but since there is no output schema, the description could do more, but given the simplicity of the tool, a 4 is reasonable.

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 all four parameters (module, function, args, request_id) are documented in the schema. The description adds that args can be a JSON object, array, scalar, or null, which is slightly more specific than the schema's 'JSON-serializable args payload'. However, this is minimal added value. Baseline 3 is correct as schema does the heavy lifting.

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 executes a local-runtime Mojo library function by module and function name, which distinguishes it from data/query APIs. However, it does not explicitly differentiate from 'execute_capability' or 'execute_decision', which may have similar execution semantics. The 'local-runtime-backed' qualifier helps distinguish it from hosted APIs.

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 mentions this surface is 'local/runtime-backed only and does not route through hosted data/query APIs,' which gives some context on when to use it. However, it does not explicitly say when NOT to use it or mention alternatives like 'execute_capability' or 'list_runtime_libraries'. The guidance is implied rather than explicit.

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