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

Goes well past the annotations (destructiveHint, non-idempotent) by disclosing the destructive scope precisely: a new mix replaces the earlier chat-made version, but downloaded versions and website mixes survive. It also documents the automatic trigger, the default mastering style (streaming when none named), and that progress/result surface in the studio.

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?

Front-loads the core action and stages in the first clause, then layers preconditions and side effects. Sentences are dense but each carries usable information; the long parenthetical at the end is slightly heavy but earns its place by scoping what gets overwritten.

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 still tells the agent where the result appears (studio shows progress and plays the result) and what state changes occur. Combined with the trigger conditions and defaults, nothing essential for correct invocation is missing.

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%, so the schema already documents songId, master and the preset enum values. The description adds only the default behavior for preset ('streaming when they name none'), which is a marginal gain over the schema; 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 concrete verb+resource+scope: mixes an existing song's stems and masters the mix, with the stage list (draft, final mix, master). It is clearly distinguishable from a plain master operation, though it never names the adjacent siblings master_song, start_mastering or adjust_mix, which is the only thing keeping it from a 5.

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 real preconditions ('a song made with create_song is already set up for this') and the trigger sequence: it waits for uploads, analysis, and the person's 'Labels are correct' before starting by itself. It also gives a use case (re-mixing with another genre or mastering style). It stops short of explicitly excluding sibling tools like adjust_mix or master_song.

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