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

Annotations only declare readOnlyHint=false, so the description carries the real burden and does add useful behavior: text tracks render in order (a later track draws over an earlier one) and presets supply complete opinionated styling. It omits any mention of what presets do to position/animation or what the call returns.

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?

Three sentences, front-loaded with placement, then preset strategy, then the length constraint. Dense with parentheticals but every sentence carries actionable information; 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 an 8-parameter mutation with a 63%-documented schema and no output schema, the description covers the decisions that actually matter: where the clip lands, how styling is chosen, and how short the text should be. Remaining gaps (timing, position) are documented in the schema itself.

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 63%, and the description meaningfully extends the schema for the most ambiguous parameters — the preset semantics (carries complete styling, override sparingly) and the track_id default. It says nothing about duration_ms, start_time_ms, position, or animation beyond what the schema already states.

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 ('Add a text clip') plus the placement rule (first text track or the one track_id names). It is clearly distinct from studio.update_text_overlay by the add-vs-modify framing, though it never names the sibling explicitly.

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 operative guidance: pick a semantic preset and override only what matters, and keep text to 5-7 words. It does not tell the agent when to use this versus studio.add_sticker or when to switch to update_text_overlay, so it stops short of explicit alternatives.

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