cache.iscached — check whether an instance is in the executor cache

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

Annotations already cover readOnly/idempotent/non-destructive, but the description goes further by disclosing that the cache library and cache.iscached are type-guarded, the call is pcall-wrapped, and the tool returns { error } rather than throwing when the library is missing or the call fails. That failure semantics is genuinely new information beyond the structured fields.

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-loaded with the purpose, then usage, then mechanics, then return/failure shape — a logical order. It is somewhat padded by repeated metadata ('Read-only' appears twice, plus 'Phase: observe; cost=medium; idempotency=read-only'), which costs it a point but does not bury the core information.

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?

No output schema exists, yet the description supplies return shapes ({ cached } or { error }), prerequisites (active-client, resolved-target, cache library present), failure handling, and even the phase/cost profile. An agent has everything needed to call and interpret this tool 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 recaps the signature and the loadstring('return ' .. expr) resolution mechanism, but that largely restates what the instancePath schema description already says ('Evaluated as `return <expression>`'), and it adds no meaning for threadContext or timeoutMs.

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 precise verb+resource ('Report whether the executor currently holds a cached reference for a single Instance') and names the exact API call it wraps (cache.iscached(inst)), which an agent can distinguish from the many other cache and inspection siblings.

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?

Explicitly says when to use it: 'confirm an instance is cached before invalidating it, or to verify that an invalidate actually dropped the cached reference', and names the paired siblings cache-invalidate / cache-replace. Both the when and the alternatives are given.

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