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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral context beyond that: it checks both directions in one request, operates by @handle, and returns relationship flags under 'data', which helps the agent understand what the tool will do and what the response will contain.

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 sentences with no wasted words. The core purpose is front-loaded, the usage guidance names alternatives explicitly, and the return location is given succinctly. Every sentence contributes distinct value.

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 simple two-parameter read-only tool with annotations, fully documented parameters, an output schema, and sibling differentiation, the description covers everything an agent needs: what it does, when to use it, what it avoids, and where the result appears. Nothing important is missing.

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 each parameter described as a screen name. The description adds meaning by clarifying that source and target are X users identified by @handle and that the tool checks the relationship in both directions, which clarifies the roles of source_user_name and target_user_name beyond the raw schema text.

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: 'Check whether one X user follows another, in both directions, by @handle.' It clearly distinguishes itself from siblings by stating that it is a single targeted lookup rather than paging through follower/following lists, and it names the exact question it answers: 'does A follow B, and does B follow A'.

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 tells the agent when to use this tool: 'Use this for a single targeted lookup instead of paging through get_twitter_user_followers or get_twitter_user_followings.' This directly names the alternatives and gives the condition for choosing this tool over them, leaving no inference required.

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