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

Annotations already declare read-only, open-world, idempotent, and non-destructive behavior. The description adds valuable details beyond annotations: billing ('1 credit + 1 credit per post returned'), page size controlled by X (no limit parameter), and pagination via meta.nextCursor. These are non-obvious behavioral traits that materially help an agent.

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 purpose, then proceeds to return format, pagination, and cost in a logical order. Every sentence contributes essential information without repetition or fluff.

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, the description adequately explains the return content (recent posts, newest first) and the meta.nextCursor pagination mechanism. Combined with annotations covering safety and the full schema, an agent has everything needed to call this 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 coverage is 100%, so the schema itself documents id and cursor thoroughly. The description adds meaning by explaining why there is no limit parameter (X chooses page size up to ~100) and reinforces cursor usage. This goes beyond the schema in explaining the absence of a common control parameter.

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 verb and resource (get timeline of a public X List) and clarifies that it returns posts from the List's members, newest first, like the feed on X. This clearly distinguishes it from siblings like get_x_list (metadata) and get_x_list_members (member list).

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 gives clear context for when to use it (to get the same feed the List shows on X) and explains pagination, but it does not explicitly name alternative tools or state when not to use it. The implied usage is strong enough for an agent to choose correctly.

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