Billing

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

The readOnlyHint=true annotation covers the safety profile, and the description adds real context beyond it: what the response contains, that limits carry a source (instance, plan, admin override), and that self-hosted deployments return an explicit 'not enabled' answer rather than an error. It stops short of stating permission requirements or what canManage implies for the caller.

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?

Front-loaded with the hosted-instance scope, which is good, but the first sentence's prose list and the second sentence's return-key list largely restate each other (plan, subscription, period, limits, limitSource, usage, watermark, plans appear twice). The self-hosted note is the one non-redundant sentence and should not be buried at the end.

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?

There is no output schema, so the description carries the return-value burden and does so by enumerating the response keys plus the top-level enabled/reason/canManage fields. With zero parameters and a read-only annotation, the remaining gaps (auth requirements, what canManage gates) are minor for a status-reading 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?

The tool takes no parameters, so there is nothing for the description to disambiguate beyond confirming it acts on the current instance without arguments. Baseline 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?

The description names the resource (billing/subscription for a hosted instance) and enumerates exactly what it reports: plan, billing period, effective limits with provenance, period usage, watermark status, and available plans. It also explicitly carves out the self-hosted case, so an agent can tell immediately whether this tool applies to the running instance.

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 context is implied by the hosting distinction ('Hosted instances…', 'On a self-hosted Reelsaw this answers that billing is not enabled'), which is genuinely useful for deciding whether it's worth calling. However, it never names the obvious alternative, billing_checkout_url, nor states the condition that selects one over the other (e.g., view status here, obtain a payment URL there).

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