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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds that this reflects the live browser session state (ephemeral, user-driven) and defines what the in/out range means, which is useful context beyond the annotations, but it says nothing about freshness, behavior when no project is open, or the shape of the response.

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?

A single front-loaded sentence that lists the three returned elements immediately, with no filler. The trailing parenthetical is slightly awkward grammatically but earns its place by explaining the range concept an agent would otherwise guess at.

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?

With no output schema, the description carries the burden of describing return contents and does so by naming the three fields an agent gets back. Combined with readOnly annotations and a single fully-documented optional parameter, nothing essential for correct invocation is missing.

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% with a single optional projectId whose description ('default: the open one') already explains the default behavior. The tool description does not mention projectId at all, so it adds no meaning beyond the schema; baseline 3 applies.

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 enumerates the concrete contents of the resource (playhead time, selected clips, marked in/out points), which tells an agent exactly what 'ui state' means and separates it from siblings like get_project or list_markers. The verb is only implied by the name rather than stated (e.g., 'returns the current...'), which keeps it from a 5.

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?

There is no explicit when-to-use or when-not-to-use statement and no named alternative. The parenthetical gloss "range; 'this part' means it" does provide indirect guidance by telling the agent to resolve vague user references like 'this part' against this tool's in/out points, which is a genuine usage hint but not a full routing rule.

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