Wrap a Luau function as a C closure and retain it

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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is structured. The description adds real value beyond that: it discloses the persistent side effect of registering the wrapper under getgenv().__mcp_closure_refs, the produced handle, and medium cost. No contradiction with the read-only annotation.

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?

Front-loads the call form and storage effect, which is good. But it carries redundancy: 'idempotency=read-only' and 'Safety: read-only' restate the same fact, and the 'Signature:' block duplicates the input schema verbatim rather than adding meaning.

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?

With no output schema, the description usefully explains what is produced (reusable Reference expression, closure metadata, created-handle) and points to tool-schema for exact fields, defaults and an invocation example. Requirements, cost and failure guidance are covered, so an agent has enough to call it 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?

Schema description coverage is 100%, so the baseline is 3. The description restates the signature with types (functionPath, threadContext, key, debugName) but adds nothing the schema does not already document via per-parameter descriptions, including the note about threadContext defaulting to the server thread.

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?

States a specific verb (wrap), resource (Luau function as a C closure), the storage side effect (getgenv().__mcp_closure_refs) and the return shape (Reference expression + closure metadata). An agent can distinguish it from siblings like new-l-closure, clone-function, and is-new-c-closure without opening a schema.

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?

Gives prerequisites ('Requires: active-client, resolved-target') and a phase/cost framing, which provides context for when it fits. However, it never names an alternative (e.g., new-l-closure for L closures) or states when NOT to use it, leaving the routing decision to inference.

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