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

Annotations already declare the mutation profile (readOnly=false, destructive=false, idempotent=false, openWorld=false). The description adds genuinely useful context: the image must be a public URL, the operation converts the post to a carousel, and there is a 10-slide cap. It does not say what happens when the cap is exceeded (error vs. silent failure) or what auth is required.

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?

A single sentence that front-loads the action and packs the effect, medium constraint, and limit with zero wasted words.

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 two-parameter mutation tool with full schema coverage and clear annotations, the description covers purpose, transformation effect, and the slide limit. The main gap is the cap-exceeded behavior and any post-type prerequisites, which are minor given the structured data already present.

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 parameters are already documented in the schema, setting the baseline at 3. The description reinforces the 'public URL' constraint on imageUrl but adds no syntax, format, or validation detail beyond what the schema provides.

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+resource ('Add an image ... to an existing post') and adds the meaningful effect: it becomes an extra slide, converting the post into a carousel with a max of 10 slides. It does not explicitly differentiate from close siblings like change_image or create_carousel, so an agent must infer the distinction.

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 phrase 'to an existing post' implies a precondition, but there is no when-to-use vs. alternative guidance. It never tells the agent how this differs from change_image (replace) or create_carousel/create_photo_carousel, which is exactly the ambiguity a sibling-heavy toolset creates.

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