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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds real value beyond that by enumerating what the response contains (plan, remaining exports, usage, credits, renewal timing) and positioning it as a pre-flight check. It doesn't say what happens when no subscription or credits are exhausted.

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, front-loaded clauses: first what the tool returns, then when to reach for it. Slightly awkward grammar ("before work their subscription may not cover") costs a little, but nothing is padded.

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 must communicate the return shape, and it does list the key data points. For a simple read-only, zero-param lookup this is nearly sufficient; only failure/lapsed-subscription behavior is unaddressed.

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 zero parameters, so the baseline is 4. The description correctly implies a no-argument call by framing it around "the person's" account rather than any input.

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 resource and scope: the person's Cardboard subscription plus remaining exports, usage, generative credits, and renewal date. No sibling in the list surfaces account/subscription data, and the description makes that distinct role obvious.

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 concrete triggering questions ("what plan am I on?", "how many exports do I have left?", upgrade intent) plus a proactive condition — call before work the subscription may not cover. It doesn't name an alternative or exclusion, but no sibling overlaps this domain.

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