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

Annotations already cover readOnly, idempotent and non-destructive, yet the description adds real substance: counts are deduplicated per address, only confirmed-and-not-stopped sign-ups count, archived transfers yield zero, and addresses are never returned. 'Reading changes nothing' merely restates readOnlyHint, so it is not a full 5.

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 purpose is front-loaded and the following sentences add edge cases and privacy behavior rather than filler. The main sentence is a long clause chain that takes effort to parse, and the closing 'Reading changes nothing' duplicates the annotation, but overall it is tight.

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 one-parameter read tool with an output schema and full annotations, the description supplies the domain semantics an agent needs: what is counted, what is excluded, and what is never returned. Return shape is rightly left to the output schema, leaving only minor gaps around usage alternatives.

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?

There is a single parameter with 100% schema coverage, so the UETR format and requirement are already fully documented. The description only implies the identifier refers to a transfer and adds no new constraint or format detail beyond the schema, matching the baseline for high coverage.

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 opens with a specific verb and resource: 'Count how many people follow a transfer's updates by email.' That is a narrow, unambiguous purpose distinguishable from get_share_link or get_payment_record. It does not explicitly name a sibling alternative, which keeps it just short of a 5.

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?

Usage is implied rather than stated: the tool counts email followers, and the description notes an archived transfer counts zero. There is no explicit 'use this when...' guidance, no statement of prerequisites, and no named alternative for related questions (e.g. listing followers or fetching a share link).

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