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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered, though the description redundantly restates "Read-only." It adds genuinely new behavior beyond the annotations: output differs by client, with widget-capable clients getting an inline preview and others a link. It stops short of noting what happens when a draft has no primary image.

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?

Roughly 45 words, front-loaded with the core action before the sibling contrast and the client-rendering caveat. Only the trailing "Read-only." is wasted since annotations already encode it.

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 an output schema present, the description needn't explain return values, and the client-dependent rendering note covers the one surprise an agent would otherwise hit. Minor gaps remain around failure modes, such as a draft with no attached image, but nothing essential for correct invocation is missing.

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%: postId is documented as the draft id and workspace_id carries detailed usage guidance including the list_workspaces fallback. The description adds nothing about either parameter, which is acceptable given the schema does the work, 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?

"Render the primary image attached to a draft on its own, without the post's text" gives a specific verb (render) and a precise scope (the image only). The following clause explicitly contrasts it with preview_post, so an agent can distinguish it from the sibling without opening either 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 names the alternative (preview_post) and states the condition that selects between them: image-only versus the whole post with the image in place. Any other sibling (preview_platform) is implicitly excluded by the draft-specific wording, so selection is unambiguous.

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