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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds only the note about the hashtag format, which is not a behavioral trait. It does not disclose return format, pagination, or any other runtime behavior beyond what annotations already imply.

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 a single, concise sentence, well front-loaded with the core purpose. However, it is concise because it is under-specified, not because it's efficiently detailed. The sentence earns its place but leaves out essential information needed for correct usage.

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 no output schema, 3 parameters (0% schema description coverage), and a description that only covers the tag format, the tool is severely underdetermined. It fails to explain what the tool returns, what values 'type' can take, or how 'token' is used. This falls far short of what an agent needs to invoke the tool 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 0%, so the description must compensate. It clarifies that 'tag' should be provided without leading '#', which is useful, but it says nothing about the 'type' or 'token' parameters. This leaves the agent guessing on how to use those parameters, even though they are optional.

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 'Posts under a hashtag (without leading #)' gives a resource (hashtag) but the verb is ambiguous—'Posts' could mean retrieving posts or creating them. It is not as explicit as 'Retrieve posts' or 'List posts under a hashtag'. It does hint at the purpose but lacks clarity and doesn't distinguish from sibling search tools.

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?

There is no guidance on when to use this tool versus alternatives like youtube_search or youtube_channel_shorts. The only usage hint is the 'without leading #' note, which is about parameter formatting, not about the tool's context or exclusions. No alternatives or preconditions are mentioned.

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