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

Annotations only say readOnlyHint=false, idempotent=false, destructive=false. The description goes well beyond that: it discloses credit spend ('Spends a few of the account's credits'), the 3-minute length ceiling, the asynchronous job return shape, and crucially what is NOT returned (no footage, sound or words). That is exactly the extra behavioral context the annotations cannot carry.

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?

Dense but front-loaded: the core action and its output come first, then cost, then the prerequisite. Some sentences are clause-heavy, but every sentence carries information an agent needs, with no filler.

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 no output schema and only one required parameter, the description has to explain the return value itself, and it does: a job whose result is the breakdown. Combined with cost, length limit, and prerequisite disclosure, an agent has everything needed to call this correctly.

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% and the single 'source' parameter is fully documented in the schema, so the description need not re-explain it. The description only hints at the library-location concept via the upload URL. Baseline 3 applies since the schema does the heavy lifting.

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 and resource (reads a reference video from the library) and enumerates the actual deliverable: hook, structure, shots, pacing and look, with still frames. This clearly distinguishes it from siblings like ugcfans_transcribe or ugcfans_make_video, which produce footage, sound or words this tool explicitly does not.

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?

Provides a concrete prerequisite ('Upload the video at https://ugc.fans/library first') and a consent condition ('confirms the person may study the file'), which is real usage context. However, it never names an alternative tool or a when-not-to-use condition, so it stops short of full routing guidance.

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