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

Annotations already declare readOnlyHint=true and openWorldHint=false, so safety is covered. The description adds meaningful context beyond the annotations by disclosing the auth requirement (organization API key) and the exact data surfaced, which is the useful behavioral detail here.

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 sentences, front-loaded with the returned data and followed by the auth constraint; nothing is wasted. Slightly less crisp because the first sentence is a bare noun list rather than an action statement.

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 and no parameters, the description must carry the return-value burden, and it does so by naming plan, usage, limit, and renewal date plus the auth requirement. Adequate for a simple read tool, though it could note that usage/limit are month-scoped quantities.

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 there is nothing to disambiguate and the baseline is 4. The description correctly adds no param detail because none exists.

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 enumerates the specific data returned: plan, entries used this month, the limit, and the Pro renewal date. An agent can tell it apart from ledger_pricing (pricing) and ledger_upgrade_pro (mutation), though the action verb is only implied by the noun list rather than stated.

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 (check your current plan/usage) and a prerequisite is given ('Requires your organization API key'), but there is no explicit when-to-use, when-not, or routing to alternatives like ledger_pricing or ledger_upgrade_pro.

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