Wrap a C closure as a Luau closure and retain it

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

The annotations already declare readOnly/idempotent/non-destructive, so the bar is lower, and the description still adds substantive behavior: the wrapper is stored under getgenv().__mcp_closure_refs, it yields a reusable Reference expression plus metadata, and it produces a created-handle. It does not say how that handle is later released (a sibling, release-closure-reference, exists), but the key side effect and return shape are disclosed.

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 core action and storage location are front-loaded in the first sentence, followed by compact labeled facts (Phase, Requires, Capabilities, Produces, Safety). The trailing 'On failure: inspect tool-schema...' line is boilerplate-ish but brief, and nothing is padded.

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 carries the burden of describing returns and it does (Reference expression plus closure metadata). Preconditions, side effects, and safety are covered; the only real gap is lifecycle guidance on releasing the retained reference.

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% and all three parameters are documented in the schema, so the baseline is 3. The description only echoes the signature ({functionPath, threadContext, key}) without adding semantics such as what threadContext defaults to or what makes a good key, leaving the schema to carry the load.

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 names the concrete action (call newlclosure, store the wrapper, return a reusable Reference expression plus closure metadata), which is specific and distinguishes it from analysis-only siblings like inspect-closure. It never states the C-closure-to-Luau-closure direction or the target-creation nature that the title carries, so an agent reading only the description could confuse it with the is-c-closure / new-c-closure family.

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 supplies preconditions (active-client, resolved-target, phase=observe, cost=medium) and a fallback pointer ('inspect tool-schema for exact fields'), which is real usage context. It never says when to prefer this over siblings such as new-c-closure, call-closure, or list-closure-references, nor when not to use it, so the guidance remains implied rather than routing.

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