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

Annotations already declare destructiveHint=true and openWorldHint=true, so the bar is lower, and the description still adds real behavioral facts: open is idempotent per sandbox and port, it requires a kept top-up, and close terminates existing connections before it returns. These are non-obvious traits not carried by the annotations. It could say more about failure modes or quota behavior, but this is solid added value.

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 resource definition, then one compact clause per action; there is little waste. The phrasing is telegraphic in places ('Needs a kept top-up', 'or one sandbox's'), which briefly costs clarity but keeps the definition short.

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 four parameters, no output schema, and annotations already covering the safety profile, the description is nearly sufficient: it scopes the tool, enumerates all three actions, maps their parameters, and even states the open return value. Only minor gaps remain, such as the return shape for list and the error behavior when a top-up is missing.

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 coverage is only 50% (action and portId are undescribed in the schema). The description compensates by mapping parameters to actions — open(sandboxId, port), list(sandboxId?), close(portId) — which the schema cannot express, and by noting that port is the in-sandbox listening port. That is meaningfully beyond the structured fields, though it adds no format or constraint detail for portId.

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 opening sentence names the concrete resource (public address:port pairs for raw TCP into a sandbox) and scopes it precisely with parenthetical examples (databases, game servers) plus the discriminating phrase 'anything not HTTP', which separates it from the HTTP-serving preview/domain siblings. Each of the three actions is then named with its verb and resource, so an agent can tell what the tool does without opening the 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?

It gives clear per-action usage context: open for exposing a listening port, list with an optional sandboxId to scope results, and close by portId. It also implies when this tool is the right choice ('anything not HTTP'). It does not, however, explicitly name an alternative sibling (e.g. the HTTP preview tool) or state when not to use it, so it stops short of full routing guidance.

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