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

Annotations already declare this as a non-destructive, read-only, closed-world operation. The description adds one genuinely new behavioral fact beyond them — that the effect is on the user's browser UI, not stored data — but says nothing about whether playback continues, whether it interrupts the user, or any constraints.

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?

One short sentence with the action front-loaded and zero redundant wording. It is efficient, though the terseness is part of why key semantics are missing.

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 two-parameter, no-output-schema tool with safety already covered by annotations, the description is nearly adequate. The unresolved time-unit ambiguity is the one gap that could cause an incorrect call.

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 only 50%: projectId is documented in the schema while 'time' is a bare number with no stated unit (seconds, frames, ticks) or valid range. This is the single most important parameter and the description does nothing to compensate for the schema gap.

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: 'Move the user's playhead in the browser'. No sibling tool manipulates the playhead, so the resource alone distinguishes it, though the description never explicitly contrasts it with view-related siblings like get_ui_state or punch_in.

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?

The parenthetical 'e.g. to show them something' hints at the intent (directing the user's attention), which implies when to use it. There is no explicit when-not guidance, no mention of what happens if no project is open, and no stated alternative.

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