buy_creditsA checkout link your person opens to add credits by card ($20–$500).
Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {
"usd": "<usd>"
},
"name": "buy_credits"
}
}| Name | Required | Description | Default |
|---|---|---|---|
| usd | Yes | Amount in USD, 20–500. |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations say this is a non-destructive, open-world write, but the description adds the crucial behavioral fact that no charge happens here — it merely produces a link the person opens themselves. That is genuine value beyond the annotations, though it omits link lifetime/expiry and what happens if the purchase is never completed.
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?
One short sentence with the outcome (checkout link) front-loaded and the amount range attached. It is efficiently sized, though the phrasing 'your person opens' is slightly informal where 'the user opens' would be clearer.
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?
For a one-parameter tool with no output schema, the description covers the essential contract: what is produced (a checkout link), who acts on it (the person), and the allowed amount range. Only minor operational details like link expiry are 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% and the single 'usd' parameter already documents the 20–500 range, so the description's '($20–$500)' merely restates it. Baseline 3 is appropriate for a fully-documented one-parameter schema.
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 names a concrete resource and outcome — a checkout link that adds credits by card — so an agent can immediately tell this is a payment/purchase flow rather than a balance read. It does not explicitly contrast with the sibling 'credits' tool (likely the balance view), leaving that distinction to be inferred from the name.
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?
Usage is only implied: when a person wants to top up credits, call this. There is no explicit when-not guidance (e.g., 'use credits to check balance first') and no note on what to do with the returned link beyond handing it over.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
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