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

Annotations (readOnly=false, destructive=false, idempotent=false, openWorld=false) cover the safety profile, and the description usefully adds that it does not publish and that passing null clears the carousel configuration, disclosing a state-changing behavior the annotations don't convey. It stops short of describing failure modes or validation errors when card count mismatches the image count.

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, each front-loaded with the operative constraint (target, cardinality rule, clear mechanism, publish boundary). No filler or repetition.

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 no output schema, the description covers the target, the required card-to-image correspondence, the clear path, and the non-publishing guarantee. Minor gaps around error handling and how the change is reflected afterward remain, but nothing critical to 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 0%, so the description must compensate, and it does: it explains that 'carousel' must contain exactly one card per current image (2-10), that cards are image-bound destinations, and that carousel:null clears. The postId meaning is only implied, keeping it just short of full coverage.

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States a specific verb (Set) plus resource (image-bound destination cards / carousel) and the exact scope (an unpublished owned Facebook post). This cleanly separates it from create_* siblings like create_carousel or create_facebook_product_carousel, which build a new carousel rather than attaching cards to an existing post.

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 clear conditions: operate on an unpublished owned post, supply exactly one card per current image within a 2-10 range, and pass carousel:null to clear. It also implicitly routes away from publishing ('Does not publish'), though it never explicitly names an alternative tool for the full publish flow.

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