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

Annotations cover the safety profile (readOnlyHint=false, destructiveHint=false, openWorldHint=true, idempotentHint=true), so the bar is lower. The description still adds real context beyond them: the operation is revision-bound (optimistic concurrency via expectedRevision), it may add a shared library voice, it debits no credits, and film speech needs separate financial approval. 'Identical operation retries retain identity' largely restates idempotentHint.

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?

Four tight sentences, front-loaded with the core action, then constraints. The retry-identity sentence duplicates the idempotentHint annotation and could be cut, but overall there is little waste.

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?

An output schema exists, so return values need not be explained. The description covers the non-obvious operational traits an agent needs — revision binding, idempotent retries, no credit debit, film-speech separation. It could say more about failure modes (e.g. revision mismatch behavior), but it is close to complete.

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 baseline is 3. The description adds only marginal framing — 'voiceId is an opaque catalogue ID' and 'expectedRevision is the current voice revision, or null when no voice exists' — which largely echoes the schema's own descriptions. No additional syntax or format detail is provided.

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+resource+source: 'Assigns an offered ready-made voice from the voice library.' This cleanly distinguishes it from siblings like studio_artist_voice_record (recording your own), studio_artist_voices_list (enumeration), and studio_artist_ready_made_choose. An agent can route to it without opening a schema.

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?

Usage is implied through scope boundaries ('creates no speech', 'Film speech requires its separate quoted financial approval'), which tells the agent when this tool is not the right one. However, no sibling alternative is named explicitly (e.g. record vs. choose vs. list), so the when-to-use guidance stays implicit.

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