Executor capability matrix (closure, Actor/state, and core primitives)

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

Annotations already declare read-only, idempotent and non-destructive, so the bar is met, yet the description adds substantive mechanics: the lookup order (getgenv() first, then thread env/_G), the dotted-name parent-table walk, and the classification rule (leaf counted available only when type=='function'). It also states the strong safety guarantee that functions are never invoked, and covers failure handling via tool-schema.

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?

Purpose and the safety guarantee are front-loaded, and the return shape is stated plainly. The long middle enumeration of ~60 probed functions is verbose, but it does define the probe's coverage boundary, which is genuinely useful for deciding whether a workflow is supported.

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 supplies the return contract ({ total, availableCount, missingCount, available[], missing[] }, both sorted, or { error }), plus phase, cost, idempotency, required context, and a failure fallback. Combined with the annotations, an agent has everything needed 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?

There is a single optional parameter and schema description coverage is 100%, so the schema already carries its meaning. The description only restates the signature ({ threadContext: number? }) without adding format, range, or effect details beyond the schema, which is the expected baseline-3 case.

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 opens with a specific verb and resource: 'probes a curated executor/runtime function list and reports which are present (callable) versus missing.' The enumerated coverage areas (reflection/closures, script access, actor discovery, hooking, etc.) make the scope concrete, but it never names the near-overlapping siblings (closure-capabilities, actor-capabilities, get-executor-info), leaving the agent to infer which capability tool to pick.

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 gives clear triggering context: 'Use this to decide up-front whether a workflow is supported, or to compare two executors.' That is a real when-to-use statement, but there is no when-not guidance and no explicit routing to alternatives when the agent only needs closure or actor coverage.

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