youtube-mcp

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It adds value by specifying the cost ('Costs 50 quota units'), which is a useful behavioral trait not inferable from the schema. However, it lacks details on permissions required, error conditions (e.g., invalid channel ID), or what happens on success (e.g., confirmation of subscription), leaving gaps in transparency.

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 front-loaded with the core purpose in the first sentence, followed by cost and parameter details in a structured 'Args:' section. Every sentence earns its place, with no redundant or verbose language, making it highly efficient and well-organized.

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 the tool's complexity (a write operation with cost implications), no annotations, and an output schema present (which likely handles return values), the description is moderately complete. It covers purpose, cost, and parameter semantics but lacks usage guidelines, full behavioral context (e.g., auth needs), and does not leverage sibling tools for differentiation, leaving room for improvement.

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?

The schema description coverage is 0%, so the description must compensate. It adds meaning by explaining that 'channel_id' is 'The channel ID to subscribe to', which clarifies the parameter's role. However, it does not provide format details (e.g., YouTube's ID structure) or examples, and with only one parameter, the baseline is 4, but the minimal explanation slightly reduces this to 3.

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 clearly states the action ('Subscribe to a YouTube channel') and identifies the resource ('YouTube channel'), making the purpose unambiguous. However, it does not explicitly differentiate this tool from its sibling 'unsubscribe', which performs the opposite action, missing an opportunity for full sibling distinction.

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 provides no guidance on when to use this tool versus alternatives like 'list_subscriptions' (to check existing subscriptions) or 'unsubscribe' (to reverse the action). It mentions a cost ('Costs 50 quota units'), which hints at resource considerations but does not specify when this operation is appropriate or necessary in context.

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