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

Beyond the annotations (non-read-only, open-world, non-idempotent), it discloses meaningful behavioral traits: a user approval round-trip yielding an approval_url, a merchant-locked mandate, a hard per-period cap, and user-initiated cancellation that permanently blocks future charges. This is exactly the operational context an agent needs before invoking a money-moving tool.

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?

The purpose and the two key constraints are front-loaded in the first two lines, followed by a compact Args block. Every sentence earns its place with no filler.

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 correctly describes what the call returns (an approval_url) and the lifecycle of the resulting mandate, and it documents all three parameters. Nothing an agent needs to select or invoke the tool correctly is missing.

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 0% and the schema even lacks an enum for interval, so the description carries the full load: it defines merchant, clarifies cap as 'max amount per period in major units' with a decimal example, and enumerates the allowed interval values ("weekly" | "monthly" | "yearly"). This meaningfully exceeds the bare schema titles.

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 and resource ('Set up a recurring subscription mandate') and immediately scopes it with a concrete example ('Netflix at up to $16/month'), which distinguishes it from one-off siblings like request_payment and record_order. An agent can tell what this does without opening the schema.

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?

It gives clear context — this is for recurring, capped, merchant-authorized charges — and states the prerequisite that the user must explicitly approve, returning an approval_url. It does not explicitly name an alternative (e.g. request_payment for one-time charges) or state when-not-to-use, so it stops short of a 5.

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