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

With no annotations, the description carries the full burden and does disclose real behavior: credits works today while usdc/anansi return payments_off (coming soon) with a quote, and upgrades prorate by counting unused days. It still omits auth requirements, cost/pricing, and whether the purchase is reversible or idempotent.

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?

Three tight sentences, no filler, with the core action and the plan/months scope front-loaded before the payment caveat. Every clause carries information an agent needs.

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?

For a mutation tool with no annotations and no output schema, the description covers the key unknowns: duration bounds, plan options, and which payment paths actually work. Remaining gaps (pricing, auth, failure behavior) are modest but real.

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%, so the description must compensate, and it does: it pins months to 1-12, defines the plan options as room/house, and explains the behavioral difference between the pay_with enum values. Only api_key semantics are left to the schema.

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 concrete verb+resource: 'Buy or extend a house plan (room | house) for 1-12 months.' It also clarifies the extend/upgrade case, which separates it from the house_plans / house_get siblings. It doesn't explicitly name those siblings, so it falls short of 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?

The description implies usage (buying a new plan vs. extending an existing one) and flags which pay_with values are currently functional, but it never names an alternative tool (e.g., house_plans to browse options first) or states prerequisites. Context 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.