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

Beyond the readOnly/openWorld annotations, it discloses two behaviors the annotations cannot convey: a fallback to the public audio page that returns only the first grid of reels, as links and cover images, and a cost of 1 credit. This is meaningful context about the data and its limits; the remaining gap is that it does not say whether pagination with cursor works in that fallback mode.

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?

The definition is short and front-loaded: it states the resource first, then the input format, then the fallback caveat, then cost. The opening two sentences overlap slightly ("Reels using a sound" / "Reels built on one audio track"), a minor redundancy, but nothing is padded.

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 read-only, open-world listing tool with no output schema, this is close to sufficient: identity of the resource, accepted identifier formats, degraded-response behavior, and credit cost are all covered. The remaining omissions are pagination behavior in fallback mode and a pointer to sibling Reels tools.

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 75%, so the schema already documents count, cursor, and audio_id; the description largely repeats the audio_id format rather than extending it. The undocumented cache_max_age parameter is not addressed anywhere, and cursor/pagination behavior is left to the schema.

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?

The description states a specific verb and resource: it lists the Reels built on a single audio track ("the 'N reels using this audio' list"). It is easy to distinguish from siblings such as instagram_reelsSearch or instagram_trendingReels based on the audio-scoped concept, but the text never names or contrasts those siblings explicitly.

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?

Usage is only implied by the prerequisite "Takes the numeric audio id or a /reels/audio/ URL"; there is no explicit "use this when..." statement, no exclusions, and no pointer to a sibling for the cases this tool does not cover. The fallback sentence hints at a degraded mode but does not say when to prefer it over an alternative.

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