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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered. The description adds the non-obvious constraint that the check is implicitly scoped to the authenticated viewer and cannot be used to test an arbitrary viewer-author pair, which is real behavioral value beyond the annotations; it stops short of noting what a negative result looks like, though the output schema covers that.

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?

Two short sentences, zero filler, with the scope constraint front-loaded before the pointer to the alternative tool. Every clause carries information the agent needs.

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?

The tool is a single-parameter read with rich annotations and a declared output schema, so return semantics need not be described. Scope, the alternative route, and the parameter's origin are all covered, leaving nothing an agent needs 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 description coverage is 100% and the single parameter's description ('Synoptic user ID of the author, such as id from get_user') already supplies format and provenance. The description adds nothing about the parameter beyond what the schema says, so the baseline 3 applies.

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+resource pair ('Check whether the signed-in user follows a given author') and immediately bounds the subject to the signed-in user, which separates it cleanly from get_following_users, follow_user, and unfollow_user in the sibling 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?

Explicitly states the scope condition ('Checks only the signed-in user') and names the alternative to use instead for a broader listing ('use get_following_users to list a user's follows'). The agent knows both when to pick this tool and which sibling to pick otherwise.

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