count_mass_entities

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower; the description still adds real value by constraining the target to the editor world (not PIE) and describing the exact return shape, which no output schema provides. It does not, however, discuss cost, timing, or refresh semantics for live entity counts.

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 and short, with scope and sibling routing up front. The only waste is that the return shape is stated twice, once inline and again in a trailing "Returns:" block, which is mildly redundant.

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 zero-parameter, read-only counting tool with no output schema, the description supplies everything needed: what is counted, which world, the return fields, and how it differs from the two neighboring mass-query tools. Nothing material 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?

Zero parameters, so the baseline is 4; there is nothing parameter-specific the description could add and it does not attempt to.

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 specific verb and resource ("Count the live Mass entities") plus a crucial scope qualifier (editor world, not a PIE world). An agent can distinguish this from the other mass tools without opening any 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?

Explicitly routes the agent: list_mass_archetypes is for fragment counts and query_mass_entities is for counting by fragment or tag, leaving this one for the plain total. The when-to-use-which decision is spelled out rather than implied.

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