list_instances

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

The readOnlyHint annotation already communicates that this is a safe read operation, so the description doesn't need to repeat that. The description adds useful scoping context about active versus archived instances but does not disclose any additional behavior such as pagination or return format. This is adequate given the annotation coverage.

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?

A single sentence that is front-loaded with the core action and resource, with zero wasted words. It is appropriately concise for a tool this simple.

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?

For a no-parameter, read-only list tool with the readOnlyHint annotation and clear sibling context, the description is complete. It covers the essential scoping (active only) and nothing relevant 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?

The tool effectively has no meaningful parameters — the input schema requires an empty wrapper object. Schema coverage is 100% since the only property is described, and the description needs to add little because there is nothing to configure. The placeholder description 'Input for the list_instances tool' is empty but not misleading.

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 uses a specific verb ('List') and resource ('active (non-archived) sandbox instances'), making the tool's function immediately clear. It also distinguishes itself from the sibling 'list_archived_instances' by explicitly scoping to non-archived instances.

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?

The phrase 'active (non-archived)' clearly implies this tool is for active instances and not for archived ones, which is a useful selection signal alongside the sibling list. However, it does not explicitly name the alternative tool or state a when-not-to-use condition, leaving a small inference gap.

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