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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so the safety profile is covered. The description adds genuinely new behavior: it answers both directions (A→B and B→A) in a single request and returns the flags under `data`. The pricing disclosure adds cost context. Minor gap: no note on what happens when a handle doesn't exist or when accounts are protected/private.

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?

Front-loaded with the core behavior followed by the routing advice, with no redundant sentences. The injected pricing block inflates the text slightly but is boilerplate rather than author padding.

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 annotations, full schema coverage, and an output schema present, the description needn't explain return values, yet it usefully points to `data`. Routing to alternatives and bidirectional semantics are covered. Edge-case behavior (nonexistent/private accounts) is the only material omission.

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%, with both source_user_name and target_user_name documented as screen names, so the baseline is 3. The description only adds 'by @handle', a small hint on identifier format, but does not clarify directionality mapping (which param is the follower vs. the followed) beyond the schema.

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 (check), resource (follow relationship), and scope (one X user follows another, both directions, by @handle). It explicitly names the sibling tools it is not (get_twitter_user_followers / get_twitter_user_followings), so an agent can distinguish it without opening schemas.

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?

Gives explicit when-to-use guidance: 'Use this for a single targeted lookup instead of paging through...'. Names the alternatives and the condition (single targeted lookup vs. paging), leaving nothing to inference.

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