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

With annotations already declaring openWorldHint=true, idempotentHint=false and destructiveHint=false, the description adds real value beyond them: expected latency (~10-20 s) and the underlying endpoint (POST /files/generate). It does not describe auth requirements, though the schema covers the email parameter.

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 dense sentence plus a short latency/endpoint note; the action, return value, and downstream use are front-loaded 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?

For a two-parameter tool with no output schema, the description covers the return artifact, timing, and downstream usage. Only minor gaps remain (no error/failure behavior), which is reasonable for this complexity.

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%, so the schema already documents both 'prompt' and 'email' fully. The description adds no syntax or format detail beyond what the schema states, so the baseline 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 ('Generate an image from a prompt') and immediately clarifies the return artifact ('an image you can see with its asset id'), which distinguishes it from sibling generators like flowmusic_cover_song or flowmusic_create_song.

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 intended usage by naming where the output goes ('refImage1..10 in flowmusic_create_song') and qualifying its role ('a loose style hint'). It lacks explicit when-not-to-use guidance, but the routing context is strong enough to pick it over siblings.

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