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

Annotations already declare this is a non-readonly, destructive, non-idempotent purchase, and the description adds real value beyond that: credits are spent immediately, USDC/ANANSI produce an invoice rather than instant provisioning, and 'house' is a placeholder that returns plan_coming_later. It does not cover failure modes (insufficient credits, invoice expiry) or how confirmation relates to confirm_subscription.

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-loads the verb, resource, and duration, then lays out payment mechanics. Every clause carries information, but the single run-on sentence with em-dashes and nested parentheses is harder to parse than a short bulleted breakdown would be.

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 a destructive-money annotation set, the description does enough: it discloses pricing, immediate vs invoiced settlement, the placeholder return for 'house', and proration on upgrades. Missing is what happens after an invoice is generated (confirm_subscription interplay) and error behavior for insufficient balance.

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?

Schema coverage is only 25%, but the description more than compensates: it explains the 'room' vs 'house' enum outcome, bounds months to 1-12, and gives per-option pricing and billing behavior for all three pay_with values. Only the api_key parameter is left to the schema, where it is already documented.

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 verb+resource with scope: 'Buy or extend a house plan for 1-12 months.' It also disambiguates the plan enum ('room' works now, 'house' returns plan_coming_later), so an agent understands exactly what it is purchasing versus browsing siblings like house_plans or house_get.

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 clear decision context for the pay_with options (credits = instant spend, usdc/anansi = Base invoice with a stated price) and notes that upgrades prorate unused days. It stops short of naming alternatives such as house_plans for listing options or topup_quote for buying credits, so routing is implied rather than explicit.

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