list_subsystem_instances

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

Annotations already cover read-only, idempotent, non-destructive behavior, but the description adds substantial context beyond them: it enumerates only editor world contexts, does not iterate LocalPlayer subsystems, and explains why (a headless editor world has no PIE LocalPlayer). It also describes the return structure, which is not covered by any output 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?

The definition is front-loaded with the core purpose, then alternatives, then scope exclusions, and finally the return shape. Every sentence earns its place; there is no filler or repetition.

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?

Although there is no output schema, the description supplies the return shape, including total, optional lifetime_filter, and the per-instance fields. Combined with annotations that cover the safety profile and explicit sibling routing, an agent has everything needed to call the 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%, and the schema already documents the optional lifetime filter with its allowed values. The description reinforces the lifetime concept via the return shape and world-context enumeration, but it does not add new syntax or filtering semantics beyond what the schema provides, so the baseline of 3 is appropriate.

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 ("Enumerate") and resource ("USubsystem instances live in the EDITOR right now") and immediately states what each entry contains (class path and lifetime). It explicitly distinguishes itself from two siblings, is_subsystem_class_active and list_local_player_subsystems, so an agent can choose without opening another 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 explicit when-to-use guidance: call is_subsystem_class_active for a yes/no on a single class, and use list_local_player_subsystems for LocalPlayer subsystems. It also states the scope condition that selects this tool: it walks the editor world context only (Engine / Editor / GameInstance / World).

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