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

Annotations already establish read-only, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuinely non-obvious domain behavior beyond that: queued items publish automatically at schedule_times, and the caveat that a draft with held_reason publish_result_unknown and reclaimed:true may already be live on Threads — a real operational gotcha. It stops short of describing pagination or ordering guarantees.

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?

Three sentences, front-loaded with the core action, then the behavioral nuance, then the triggering use case. Dense but every clause carries information; the held_reason sentence is slightly jargon-heavy but justified by the risk it flags.

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, and the description compensates by naming the return fields an agent needs (per-item position and next_publish_at). Combined with the annotation safety profile and full schema coverage, an agent has enough to call this correctly; ordering/pagination semantics remain unstated.

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%, so both the status enum values and the 'max 200' limit are already documented structurally; the description largely restates them. It does add meaning to status by explaining what 'queued' behaviorally implies (auto-publish at schedule_times) and what a 'draft' state can signify, which is a modest value-add over the schema.

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?

Opens with a specific verb+resource+scope: 'Lists an account's library items by status', and enumerates the status values. It doesn't name a sibling to distinguish itself from (e.g. list_schedules, list_pending_replies, bulk_queue_library), so an agent must infer the boundary from the usage sentence rather than an explicit contrast.

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 final sentence gives concrete triggering conditions: 'what is queued, what is waiting as a draft, or what failed.' That is clear positive guidance with no exclusions or named alternatives, so it lands at 4 rather than 5.

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