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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety and mutation profile is covered. The description adds behavioral context beyond annotations: it clarifies that the tool returns long-form videos (excluding Shorts), returns a list, and uses a cursor for pagination. It doesn't contradict annotations and gives useful expectations about result structure and pagination.

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?

The description is three short sentences, each carrying essential information: purpose, exclusion/alternative, and input/output/pagination. It is front-loaded with the core action and immediately resolves the most likely ambiguity (Shorts vs long-form). No redundant words.

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 list tool with five optional parameters and no output schema, the description covers the essential behavior: what it lists, the key input options, and pagination. It doesn't explain sortBy or includeExtras, but those are fully described in the schema. It also lacks explicit note that channelId and handle are mutually exclusive, though 'or' implies it. Given the annotations and schema coverage, the description is sufficiently complete for an agent to call it correctly.

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 every parameter has a schema description. The tool description adds meaning beyond that: it clarifies that either channelId or handle can be used (implied by 'Accepts a channel id or handle') and explains cursor usage ('use cursor when paginated'). This supplements the schema's generic descriptions, especially for cursor and the channel identifier selection.

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 action: 'List long-form videos from a YouTube channel', and immediately distinguishes itself from a sibling by saying 'not Shorts — use youtube.channel.shorts.list'. It also specifies input scope ('Accepts a channel id or handle') and output type ('Returns a list'). This clearly differentiates it from youtube_channel_get (channel metadata) and youtube_channel_shorts_list (Shorts).

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 description explicitly provides a when-not-to-use and alternative: 'not Shorts — use youtube.channel.shorts.list'. It also gives input usage ('Accepts a channel id or handle') and pagination guidance ('use cursor when paginated'). This is direct and actionable for an agent deciding between tools.

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