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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the safety profile is known. The description adds real context beyond them: irreversibility ("cannot be undone"), the return value ("Returns the deleted id"), and cost ("Uses no credits"). It stops short of error behavior (e.g., unknown id, items in use elsewhere), which keeps it at 4.

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?

Four short sentences, each carrying distinct information: action, irreversibility, alternative routing, return/cost. The permanence warning is front-loaded and nothing is padded.

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 single-parameter delete with no output schema, the description covers the destructive nature, the irreversibility, the fallback tool for drafts, the returned value, and credit cost. An agent has everything needed to call it correctly and safely.

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 description coverage is 100% and the single id parameter is already documented as "The library item id from list_library." The description's "by its id" restates rather than enriches that, 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?

"Permanently deletes one item from the creator's library by its id" gives a specific verb (deletes), resource (library item), cardinality (one), and key (id). It also names the sibling it is not (discard_draft), so an agent can distinguish it 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?

The description explicitly routes usage: "Use it for saved items; for unsaved drafts use discard_draft." That is a concrete when-to-use plus a named alternative with the condition that selects it.

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