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

With no annotations, the description carries the full burden and does well on rendering behavior: white text on a translucent dark box, font_size 0 meaning ~1/18 of frame height, and start/end defaulting to the whole video. What it omits is the outcome side — whether a new video artifact is produced or the source is modified in place, and how that result is returned — which matters for a tool with no output schema.

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-loaded with the operation, then a compact block of parameter facts, each sentence adding new information with no repetition. Nothing here is 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 a 6-parameter, annotation-free media tool the input side is thoroughly covered, including sentinel-value meanings the schema leaves opaque. The remaining gap is the return contract — output artifact and any processing/error behavior — which the absence of an output schema pushes onto the description.

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 0%, so the description must compensate, and it does: it enumerates the valid position values, explains that font_size 0 means auto with a concrete ratio, clarifies that the schema's -1 defaults for start_s/end_s mean "whole video," and states the 300-character limit and \n line-break convention for text. Only url is left unexplained, which is self-evident.

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 opening sentence gives a specific verb plus resource plus medium: "Burn a text caption/title into a video." That is unambiguous and clearly distinct from siblings like video_add_audio, video_concat, or video_trim, so an agent can pick it without inspecting other schemas.

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 by the name and the description of what gets rendered, but there is no explicit statement of when to choose this over alternatives, and no prerequisites are given (e.g., that url must be a reachable video, or whether this is a heavy/async render). The agent must infer context.

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