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

Goes well beyond the readOnlyHint annotation by disclosing the full side-effect model: it only returns a URL, nothing is charged before the user pays, and the agent must not claim subscription or quote prices. This is exactly the kind of context annotations cannot carry.

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-loaded with the usage trigger, then consequences, then parameter semantics. Every sentence is load-bearing and none repeats structured fields verbatim.

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?

An output schema exists so return values need no elaboration, and the description covers triggers, side-effect boundaries, parameter meaning, and pricing behavior. Nothing needed to invoke it 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 100%, so the baseline is 3, but the description adds real meaning the schema lacks — 'credits' is a legacy name and only applies to users who already have a paid plan, and 'monthly' is the default. It clarifies the enum beyond the schema's terse 'Default monthly'.

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 action (obtaining a paid plan) with concrete triggers and names the exact artifact returned (upgrade_url). No sibling tool overlaps with plan upgrades, so differentiation is inherent. An agent can identify this tool's function immediately.

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?

Explicitly lists the trigger conditions ('wants a paid Kleap plan, runs out of usage, or needs a feature that requires one') and adds behavioral guardrails ('never say they are subscribed', 'do not quote a price'). What is left is only the absence of a named alternative tool, which isn't needed since no sibling performs upgrades.

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