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

Annotations indicate readOnly=false, openWorld=true, and idempotent=false, and the description adds concrete side effects: a Stripe Checkout session is created, the link expires in ~24h, and agents never handle card details. It also clarifies pricing is computed server-side, which is non-obvious and prevents agents from trying to calculate prices themselves.

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 sentences front-load the action and return contract, then add exactly the operational details an agent needs: who pays, what to pass to send_fax, and expiry. There is no filler and no repetition of schema content.

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?

Given no output schema, the description names the two key return values, payment_url and payment_id, and links them to the surrounding human-payment and send_fax flow. The expiry guidance and server-side pricing fill the practical gaps for a 4-parameter tool, making it complete enough to call correctly.

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?

All four parameters already have descriptive schema text (100% coverage), so the description need not repeat them. It adds only cross-cutting behavior such as server-side price computation and the expires_at signal, rather than per-parameter semantics, matching the baseline for fully covered schemas.

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 ('Create a Stripe Checkout payment link for a fax') and distinguishes itself from siblings by explaining that the returned payment_id is later passed to send_fax. It is unmistakably a payment-setup tool, not a quote, status, or send tool.

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 frames the exact workflow: give payment_url to the human, wait for payment, then pass payment_id to send_fax. It also advises creating a fresh link if the human delays because the link expires. It does not explicitly contrast with get_fax_quote, so exclusions are left implied rather than stated.

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