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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=false, so safety is covered. The description adds interaction-sequencing behavior (list the index first) and a batching rationale (avoid serial probes) that annotations do not convey. It does not describe cursor/pagination behavior, which limits it to a 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?

A single front-loaded sentence with no filler: action, cap, sequencing, and the anti-pattern are all packed in and the most important constraint leads.

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?

An output schema exists, so return values need not be explained, and the batch semantics plus sequencing are covered. The unexplained optional cursor (pagination) is the one meaningful omission for a batch fetch with a cursor field.

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 carry parameter meaning. 'selected ... after listing the index' helpfully implies media_refs are references obtained from account_media_list, and the 50-item cap aligns with maxItems. However, ad_account_id and especially the cursor parameter are not explained anywhere, leaving real gaps.

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 ('Fetch'), resource ('account media previews'), scope ('up to 50 ... in a batch'), and sequencing ('after listing the index; avoid serial item probes'). This implicitly but clearly separates it from the single-item sibling account_media_get and the index tool account_media_list.

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?

Tells the agent when to reach for it ('after listing the index') and what to avoid ('serial item probes'), which is actionable context. It stops short of naming account_media_get / account_media_list as explicit alternatives, but the intended usage pattern is clear.

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