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

Annotations already declare this is a non-destructive write operation. The description adds useful behavior beyond the annotations by disclosing persistence ('Kept in the session and a sidecar') and downstream consumption by chapters and pipeline.

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?

Two short sentences with no wasted words. The core action is front-loaded, followed immediately by persistence and downstream behavior.

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?

Given that annotations, a fully documented schema, and an output schema are present, the description supplies the key missing context: markers persist in session and sidecar and feed chapters/pipeline. It does not elaborate on permissions or error behavior, but little is missing for a simple marking tool.

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%, so the detailed parameter meanings are already documented in the schema. The description adds only the high-level distinction between live marking and marking at a second, which is useful but not more specific than the 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 verb and resource ('Mark a labelled moment on a recording') plus the two modes ('live or at a second'). It also differentiates markers from the sibling 'chapters' tool by explaining that 'chapters and pipeline turn markers into chapters.'

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 gives clear context for when this is appropriate: while recording live or at a specific second. It does not state explicit exclusions or name a direct alternative, but the consumer relationship with 'chapters' and 'pipeline' makes the intended workflow clear.

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