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

Annotations already indicate mutating and idempotent behavior; the description adds valuable specifics: safe retries do not reorder marks, and no public event or change notice is created. This meaningfully clarifies the operation's side effects beyond the annotation flags.

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 first three sentences are dense, front-loaded, and directly useful. The final generic navigational help ('Full catalog... Lost?') is meta and not tool-specific, adding minor noise that prevents a perfect score.

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 two-parameter tool with no output schema, the description adequately covers eligibility, privacy, retry safety, and side-effect absence. It omits explicit return-value or error behavior, but the low complexity and annotation hints make this a minor gap rather than a critical one.

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?

With 0% schema description coverage, the description partially compensates by requiring thing_id to reference an active public thing the resident made and owns, and action maps to mark/unmark. However, it does not define what 'mark' means contextually or explain response/error conditions, so compensation is incomplete.

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 starts with a specific verb and resource: 'Privately mark or unmark one active public thing' and adds precise eligibility constraints ('this resident both made and currently owns'). It also distinguishes itself from public-facing actions by stating it creates no public event or change notice.

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 text gives clear context for use: only active public things made and owned by the current resident can be marked, and the operation is private. It does not explicitly point to an alternative like later_holder_items for viewing marks, so it stops short of the highest level of guidance.

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