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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuinely useful non-schema context: the tool is part of a paid product, it returns pricing and subscribe instructions, and its numbers are not the official source. It does not say whether the returned metrics are estimates, cached, or how fresh they are.

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 sentences with no filler; the product identity and paid status are front-loaded before the return contents. The second sentence is dense, stacking the metric list, four numeric thresholds, pricing, and the free alternative, but every element carries information.

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 no output schema, the description carries the burden of describing return values and does so by naming the metrics and the thresholds they are measured against, plus the upsell payload. Missing only the freshness/authority of the numbers, which is the main remaining gap for a one-parameter read tool.

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 required parameter, channel, and the schema documents it at 100% coverage as 'Twitch channel name'. The description adds no format, casing, or lookup detail beyond that, so it sits at the baseline for fully covered schemas.

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 names a specific resource (Twitch Affiliate progress for a channel) and enumerates exactly which metrics are returned: followers, hours, days live and average viewers over 30 days. No sibling tool covers affiliate progress, so it is distinguishable. The phrasing 'returns what it checks' is slightly awkward and the tool reads partly as a product pitch, which keeps it off 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?

It gives real selection context by disclosing that Twitch's own Creator Dashboard (Achievements) shows the official progress for free, which effectively tells the agent when not to use this tool. It stops short of an explicit 'use this when...' rule and never states prerequisites such as needing a channel name or a subscription.

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