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

Annotations already cover the safety profile (readOnly, non-destructive, closed-world), and the description adds value beyond them: it discloses the cost model ('Uses no credits') and that the result is tagged with kind library or draft. It does not cover failure behavior for a missing or cross-account id, which keeps it from a 5.

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 short sentences, front-loaded with the operation and return payload before the usage hint. The clause 'Returns item, with kind library or draft' is slightly clipped/awkward but carries real information, so there is little waste.

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?

With no output schema, the description correctly takes on the burden of describing return fields, naming the major content attributes and the kind discriminator. For a one-parameter read tool this is nearly complete; only error/not-found and draft-vs-item resolution are unaddressed.

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% for the single id parameter, so the schema already documents it fully. The description reinforces that the id can address either a library item or a draft, but adds no format, sourcing, or lookup guidance beyond that. 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?

States a specific verb and resource ('Returns one library item or draft in full by its id') and immediately enumerates the payload (text, hooks, call to action, on-screen hook, caption, notes, content pillar, funnel stage), so the agent knows exactly what it gets. This is clearly distinguishable from list_library (paged summaries) and update_library_item (mutation).

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?

Gives concrete usage context: call it after list_library or generate_content when the full piece is needed, which implicitly routes list-style needs elsewhere. It does not state explicit exclusions (e.g., when to use get_generation instead of fetching a draft), so it falls short of a full when/when-not statement.

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