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

Annotations already declare the safety profile (destructiveHint=true, idempotentHint=false, openWorldHint=true), so the bar is lower. The description still adds non-annotation value: a concrete quota cost (1600 units) and patch semantics ('Only fields provided are changed'), which tells the agent this is not a full-replace operation. It omits auth scope and whether prior values can be restored.

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?

Three short sentences, front-loaded with the operation and fields, followed by cost and patch semantics. No filler or redundancy.

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-param mutation tool with no output schema, the description plus annotations cover the essentials: what changes, that it is a patch, and the quota price. Missing only peripheral details such as required permission scope or confirmation/rollback behavior.

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% and each property already documents 'Omit to keep current', so the description's field list largely duplicates the schema. The one added nuance, that only supplied fields change, is genuinely parameter-relevant, but it does not compensate beyond the baseline.

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 (update) and resource (YouTube video) plus the exact mutable fields (title, description, privacy, tags). This clearly separates it from siblings like youtube_delete_video, youtube_upload_video, and youtube_video_query without needing to open any schema.

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 verb and the patch note, but the description never states when to prefer this over alternatives (e.g. youtube_upload_video for new content) or any prerequisites such as ownership/auth. The quota-cost line is useful decision input but is not a when-to-use rule.

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