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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false, and openWorldHint=false, so safety is covered. The description contributes some behavioral context by naming what portion of a lecture is returned (only words 'at its start', not the full transcript), but says nothing about cost, permissions, or what happens with a malformed id. With annotations carrying the safety profile, a 3 is appropriate.

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?

It is a single sentence with no filler, but it is syntactically tangled — a colon-introduced list of return fields embedded in a disjunction about id types. The most decision-relevant fact (a moment id is '<lecture id>@<second>') is buried mid-sentence rather than front-loaded.

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 one required parameter, full schema coverage, complete annotations, and an output schema to describe return values, the description covers what the agent still needs: which id forms are accepted and roughly what a moment record contains. Nothing required to call it correctly 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 coverage is 100% for the single id parameter, so the baseline is 3. The description earns an extra point by revealing the concrete moment-id format '<lecture id>@<second>', which the schema does not spell out, and by restating that a page address is also acceptable.

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 makes clear this returns a single lecture moment (or a whole lecture) with its title, summary, answered questions, opening transcript, lecture/credit line, and playback URL. That is a specific resource with an enumerated payload, well beyond the generic name 'fetch'. It stops short of a 5 because it never distinguishes itself from the sibling get_lecture, even though it explicitly accepts a lecture id as input.

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 only implied: 'One result of search by its id' hints that this is the follow-up to a search call, but no sentence says when to prefer this over search_moments, get_lecture, or get_topic. There are no exclusions or prerequisites stated, leaving the agent to infer the routing.

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