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

Annotations already declare readOnlyHint=true, and the description reinforces that with "Free." and the quote-not-charge framing. It adds a genuine behavioral constraint (captions on a song are always whole lines, never word sync), which is real output-shaping context. However it doesn't explain what happens when the quote doesn't fit (fits/blockers/warnings fields are named but not described), so added behavioral depth is partial.

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 key fact ("Free."), then the workflow handoff, then a compact Args/Returns block. Almost every sentence earns its place. Minor waste in restating Args that the schema already covers, and the phrasing of the opening sentence is denser than needed.

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?

Though there is no output schema, the description enumerates the return shape (ok, quote with render_cents, outstanding_cents, fits, blockers, warnings, items, plus music_plan), which is enough for an agent to consume the result. For a read-only two-parameter tool with a nested pass-through plan object, this is close to complete, with only the meaning of fits/blockers left implicit.

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 both parameters are already documented, and the description repeats essentially the same information (song_id and music_plan from music_video_director).'a read song' is a less informative gloss than the schema's own pattern and pointer. Baseline 3 applies since the schema carries the semantics.

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 conveys a specific verb and resource: it returns the server-side price quote for a plan, plus the normalized plan. The trailing note about passing quote.render_cents to studio_render further pins down what this step is in the workflow. The opening phrasing ("The server quote for a plan and the plan as the server made it") is slightly indirect rather than a clean "estimate the render cost of a plan", but an agent can still identify the operation.

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?

It states the upstream source (music_plan comes from music_video_director) and the downstream handoff (pass quote.render_cents to studio_render as confirm_cents), which effectively defines when to use it: between directing and rendering. No explicit exclusion, but the sequencing makes the alternative implicit and clear.

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