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

With no annotations, the description carries the full burden and does well: it discloses the one-time key return, the Bearer auth format, the enum constraint rationale (Stripe's fee), bonus percentages, and that bonus credit is never refunded. It omits failure/idempotency behavior for a payment call (e.g., whether a retry double-charges), which is the main remaining gap.

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?

Dense but every sentence carries information; no filler. Structure is slightly back-loaded — the critical save-the-key-ONCE warning sits mid-paragraph rather than being front-loaded, but nothing is wasted.

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?

No annotations and no output schema, so the description must self-describe, and it covers mechanism, key lifecycle, spend tiers, and refund policy. Only edge-case behavior (errors, retries, expired SPT) is left undefined for a payment tool.

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 only 50%, so the description must compensate. It adds real meaning for amount_usd by explaining the allowed values exist because smaller amounts lose money to Stripe's fee, and it clarifies spt's origin (Link session approval). This is more than the schema alone conveys.

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 precise verb and resource ('Add shop credits') plus the payment mechanism (Stripe Shared Payment Token). It is immediately distinguishable from the sibling credits_balance (a read) without opening any 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?

Explains the two invocation modes: no existing key → opens a new account and returns a new key; valid key present → tops up that account. It gives clear context for when each path applies, though it never names an alternative tool or states an explicit when-not-to-use.

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