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

Annotations already declare readOnlyHint=true, so the read-only nature is covered. The description adds behavioral value by explaining that each instance represents per-user accumulated events and why a digest might be pending (still accumulating or empty). This goes beyond the annotation's basic safety hint and helps the agent interpret the results.

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 description is a single sentence but packs the core action, a definition of instances, and a diagnostic rationale without redundancy. It is front-loaded with the primary purpose and remains readable. While not overly concise, it uses structure well and contains no filler.

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?

There is no output schema, so the description must convey what to expect. It explains the nature of instances and the diagnostic value, which is largely sufficient for a list operation. It does not describe ordering or explicit pagination semantics, but the cursor parameter is already documented in the schema. Overall, the description covers the essential context.

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 100%, and the schema descriptions for limit, cursor, and schedule_id are already detailed (defaults, caps, format, and opaque-token warnings). The tool description does not add parameter-specific semantics beyond what the schema provides, so the baseline 3 applies.

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 clearly states the verb (List), the resource (digest instances), and defines what an instance is ('events accumulated so far for one user against that schedule'). It also explains the purpose (shows what is waiting to go out, answers why a digest hasn't arrived). This is specific and distinguishes it from related tools like release_digest.

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 description gives clear context for when to use this tool: to inspect what is waiting to go out and diagnose non-arrival. It implicitly distinguishes from release tools by focusing on inspection. However, it does not explicitly name alternatives or state when not to use it, so it falls short of the 5-level criterion.

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