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

Adds two behavioral facts the annotations cannot express: the image_url path downloads into the media library (a side effect beyond the post mutation), and the 'Through Royally' sentence discloses that the operation is queued for human approval and nothing on the site changes until then — critical for interpreting a success response and for why destructiveHint=true. This is exactly the added context annotations leave out.

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?

Front-loaded with the action and the either/or operand rule, then the approval caveat last where it matters. Minor waste: the '(site: demo.royalplugins.com)' parenthetical repeats the site_id description already present in the schema.

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?

Covers inputs, side effects, removal, and the approval gate, which is sufficient for a mutation tool with no output schema. It does not say how the agent can later confirm approval (e.g. via mcp_list_recent_changes or get_execution), leaving the outcome-check loop implicit.

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 baseline is 3, but the description adds the mutual exclusivity between media_id and image_url (not encoded as oneOf in the schema) and the sentinel value media_id=0 for removal. It also notes alt_text applies to both input paths.

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 ('Set or replace the featured image on a post or page') plus the two accepted input modes and the removal case. No sibling in this fleet performs this operation, so the definition has no ambiguity to resolve.

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?

Explicitly routes the agent to wp_get_media for an existing media_id and reserves image_url for images that must be downloaded first, and it states the media_id=0 removal path. It stops short of naming any alternative/fallback (e.g. wp_update_media for attachment fields), but the operand selection guidance is clear.

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