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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, yet the description still adds substantive operational context: a 30-per-hour browsing quota and the fact that private accounts yield an empty result rather than an error. That rate-limit and empty-result disclosure is exactly the kind of information an agent needs and cannot get from the annotations alone.

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?

Four short sentences, front-loaded with the resource definition and followed by the constraint facts in descending importance. The telegraphic style ("Private accounts show nothing") is efficient rather than cryptic, though it borders on note-form.

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 four-parameter read tool with a 25-item page cap and no output schema, the description covers purpose, the alternate-subject parameter, the rate limit and the notable private-account edge case. Pagination mechanics and what a follower record contains are the only omissions, and cursor semantics are handled by the schema.

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 75% and the schema already documents limit, cursor and user_id. The description nonetheless adds real meaning: usernames are accepted on Instagram for user_id, and the effective page cap is 25 regardless of the schema's maximum of 100. Only cursor behavior goes unexplained, and the schema covers it.

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?

Identifies the resource precisely ("People who follow the account") and the scope variation via user_id, which lets an agent distinguish it from list_following or list_follow_requests. The verb is implicit (a list operation) rather than stated, but the resource and direction of the relationship are unambiguous.

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 practical conditions: use user_id (or a username on Instagram) to target another person, and expect nothing for private accounts. It does not explicitly route the agent between this and the adjacent list_following / list_follow_requests siblings, so the when-not guidance is only implied by the resource wording.

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