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

Annotations declare readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false, but the description adds crucial context the agent can't get from them: the tool itself never modifies the subscription or charges anything, everything completes on Stripe's hosted pages, and links expire after a few minutes. This is exactly the added value expected beyond annotations.

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 most important facts (secure link, no direct mutation) are front-loaded and each sentence earns its place. It is slightly dense with parenthetical pricing detail, but nothing is redundant.

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 still tells the agent what is returned (a shareable link) and its expiry behavior, and it covers both modes and the auto-routing edge case. Nothing needed to call this correctly appears to be 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 meaning not present in the schema: concrete plan tiers with prices (£12/£29/£99/£299) and the ~20% annual saving plus the monthly default for billing_cycle. The enum values themselves are already in the schema, so it stops short of a 5.

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?

The description states a specific verb and resource — 'Get a secure Stripe link' for upgrading or managing the ScriptGrain plan — and cleanly separates the two modes (checkout link vs billing-portal link). The sibling get_billing is distinguishable because this tool mints an upgrade/manage link rather than reading billing data.

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 explicit when-to-use conditions: pass plan when a free account hits a credit wall, omit plan to manage an existing subscription. It also names a routing rule (already-subscribed accounts asking for checkout are sent to the portal), leaving little to inference.

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