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

The description reveals that it reads actual frames, returns exact rectangles as frame fractions, and includes visibility times. It also notes project-scoping and that the project identity is returned. Annotations already declare readOnlyHint=true and destructiveHint=false, so the description adds valuable detail about output format and scope without contradicting them.

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?

The description is a single dense paragraph where each sentence contributes: scoping, purpose, behavioral detail, alternative usage, read-only note, and parameter explanations. No filler or redundancy; it is appropriately front-loaded with the most critical scoping constraint.

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?

The description covers purpose, usage alternatives, behavioral expectations, and parameter semantics. It even specifies the return format (exact rectangles as frame fractions, visibility times) despite having no output schema. The only minor gap is that start/end units are not explicitly stated, but 'source-time window' strongly implies seconds, so the tool is sufficiently complete for correct invocation.

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?

With only 25% schema description coverage, the description compensates by explaining the scope enum values (captions, watermark, text, all) with their meanings, describes start/end as a source-time window, and gives specific guidance for project_id (copy from list_projects/open_project/project_state, never guess from active pointer). This adds meaning beyond the bare schema.

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 states a specific action (measure where text is burned into footage), lists concrete examples (subtitle bands, watermarks, handles, on-screen labels), and explicitly contrasts with look_at for estimating rectangles, making the tool's purpose unambiguous and distinct from siblings.

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 directly instructs 'Use this INSTEAD of estimating a rectangle from look_at' and explains the consequence of using the alternative. It also defines each scope value (captions, watermark, text, all) with behavioral distinctions, providing clear when-to-use guidance.

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