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

Annotations already declare the non-read-only, non-idempotent profile, and the description adds genuinely useful context: the operation is asynchronous ('returns a job'), it is priced ('Free of credits'), it is capped at 10 minutes, and it enumerates the result fields (transcript id, text, language, length). It does not mention how to await the job despite siblings ugcfans_get_job and ugcfans_wait_job existing, which is the one notable gap.

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?

Effectively two sentences, front-loaded with the action and constraints, then the cost and workflow hints. Dense but every clause carries information; the only slight awkwardness is a long compound first sentence.

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, the description compensates by describing the async job return and the eventual result fields. Combined with the prerequisite upload/discovery steps and the size limit, an agent has everything needed to call it 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 description coverage is 100% and there is only one parameter, whose schema description ('The file's address in the library, out/...') matches the description's phrasing. The description repeats the library-address concept without adding syntax or format detail beyond the schema, so the baseline of 3 applies.

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 ('Writes out the words of an audio or video file in the library') with concrete scope (max 10 minutes, built-in speech model). It clearly distinguishes itself from adjacent tools by naming ugcfans_list_files as the way to obtain the input and ugcfans_finish_clip as the downstream consumer.

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 an explicit prerequisite workflow: upload to https://ugc.fans/library first, then resolve the address with ugcfans_list_files. It also tells the agent what to do with the result (transcript id feeds captions in ugcfans_finish_clip). It stops short of stating when transcription is unnecessary or naming an alternative transcription path, but as the only transcribe tool the routing need is low.

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