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

Annotations only say readOnly/openWorld/non-destructive; the description goes much further, explaining that a URL must be opened by the user to pay, that the result carries price and discount, and that changePlan=true means a prorated subscription change with unused days credited and preview.amountDue charged today (or nothing during a trial). This is exactly the kind of consequence-level context the annotations cannot convey.

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?

Purpose is front-loaded in the first clause and the return/changePlan semantics follow logically. The dense unpunctuated run of plan features in one parenthetical is heavy to parse, but nearly every clause carries decision-relevant information.

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 only two enum parameters and no output schema, the description covers everything needed: what the call returns (URL, price, discount), the meaning of changePlan and preview.amountDue, trial behavior, and who handles downgrades. An agent can call this and explain the result to a user without further guessing.

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; the description adds real meaning by spelling out what each plan actually entitles the user to (accounts, executions/day, backtest horizon, MetaTrader access) and that yearly billing is cheaper than monthly. That helps the agent pick and justify a plan value rather than just echoing the enum.

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 ('Get a Stripe checkout URL') plus the exact object of the action ('upgrade the user's TraderWAI plan'). No sibling tool touches billing/subscription, so the boundary is unambiguous on name alone.

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 useful routing context: 'PLUS only when it is on sale: the plan-limit messages say which plan to offer' and an explicit when-not — 'Downgrades are done by the user on the pricing page.' It lacks a crisp statement of the triggering condition (e.g., when the user hits a plan limit or asks to upgrade), so it stops short of a full 5.

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