# MCP use case: refunds with the business rules in the route > The refund policy (30 days for any reason, damaged items at any time, a £500 limit, never more than was paid) is enforced by the `issue_refund` route, not by the prompt. When a rule says no, the route refuses in plain words and Claude passes the reason on; it did not split a £900 refund to get under the limit. In the field test, all 20 refund runs were correct. **Cargo feature:** [`ai`](../build-features.md) · **Example:** [`examples/agents/mcp-shop`](https://github.com/pmsudhi/cameleer/tree/main/examples/agents/mcp-shop) · **Part of:** [Cameleer MCP](../mcp.md) ## What people ask, and what happens Every refund also asks the user to approve it ([approvals](approvals.md)). | request | tool calls (recorded run) | what happened | |---|---|---| | Refund order 1011, the jacket was the wrong size. | `get_order`, `issue_refund` | approved, £159 refunded (RF-1): delivered 10 days ago, inside the window | | Refund order 1002, they didn't like it. | `get_order`, `read_document` | not refunded: delivered 45 days ago; Claude offered store credit or a repair, as the policy says | | The hiking boots on 1015 fell apart after a week, refund just the boots. | `get_order`, `issue_refund` | £179 for the boots only, marked defective; the socks stay paid | | Refund $900 on order 1020. | `get_order`, `read_document` | not refunded: over the £500 limit, a manager must do it; Claude also asked whether "$" meant pounds | | Aisha Bello complained that her stove arrived with a cracked burner. Refund her latest order. | `search_customers`, `list_orders`, `get_order` | the order also has a pot: Claude asked whether to refund the stove (£119) or all of it (£164) | ## A recorded conversation **User:** The hiking boots on 1015 fell apart after a week, refund just the boots. Claude read the order, then called `issue_refund` with `{"orderId": 1015, "amount": 179, "damagedOrDefective": true, "reason": "Defective: Ridgeline Hiking Boots (BOOT-HK) fell apart after a week of use"}`. The user approved the form and the route wrote the refund: > I refunded £179.00 for the Ridgeline Hiking Boots on order 1015, which is Hana Sato's order. > The refund ID is RF-1. [...] The 3 pairs of Merino Hiking Socks (£54.00) weren't refunded, > so £54.00 of the £233.00 order total is still paid. When Claude does call the tool against a rule, the route answers with an error result, for example: > Order 1002 was delivered 45 days ago, outside the 30-day refund window. Only damaged or > defective items can be refunded after 30 days (policy://refunds); otherwise offer store > credit (issue_store_credit, needs a manager) or a repair. ## How the tool is built The route loads the order, computes the days since delivery in the embedded SQL engine, and checks each rule in order. Each refusal sets `CamelAiToolIsError` and says what to do instead: ```yaml - route: id: issue-refund from: uri: ai-tool:issue_refund parameters: title: Refund an order description: >- Refund a delivered order, in full or in part. Follows the refund policy (resource policy://refunds): within 30 days of delivery for any reason; damaged or defective items at any time; refunds over 500 need a manager and are refused here. Give the amount for a partial refund (for example the price of one item); without it the remaining amount is refunded. Needs the user's approval. tags: acme parameter.orderId: integer parameter.orderId.description: The order number parameter.orderId.required: true parameter.reason: string parameter.reason.description: Why, such as "wrong size" or "damaged on arrival" parameter.reason.required: true parameter.damagedOrDefective: boolean parameter.damagedOrDefective.description: True when the item arrived damaged or turned out defective parameter.amount: number parameter.amount.description: Amount to refund for a partial refund; omit for everything not yet refunded destructiveHint: true steps: - to: direct:load-order - setHeader: name: amt simple: "${header.amount ?: ${header.remaining}}" - to: "sql:select case when :#orderDelivered is null or :#orderDelivered = '' then -1 else cast(date '{{acme.today}}' - cast(:#orderDelivered as date) as int) end?dataSource=jdbc:rustsql:mem:acme&outputType=SelectOne" - setHeader: name: daysSince simple: "${body}" - choice: when: - simple: "${header.order} == null" steps: - setHeader: name: CamelAiToolIsError constant: true - setBody: simple: "Order ${header.orderId} does not exist." - simple: "${header.orderStatus} != 'delivered'" steps: - setHeader: name: CamelAiToolIsError constant: true - setBody: simple: "Order ${header.orderId} is ${header.orderStatus}; only delivered orders are refunded here. Orders that have not shipped can be cancelled instead (cancel_order)." - simple: "${header.remaining} <= 0" steps: - setHeader: name: CamelAiToolIsError constant: true - setBody: simple: "Order ${header.orderId} has already been refunded in full." - simple: "${header.amt} <= 0 || ${header.amt} > ${header.remaining}" steps: - setHeader: name: CamelAiToolIsError constant: true - setBody: simple: "The amount must be more than 0 and at most ${header.remaining}, the part of order ${header.orderId} not yet refunded." - simple: "${header.amt} > 500" steps: - setHeader: name: CamelAiToolIsError constant: true - setBody: simple: "Refunds over 500 need a manager's approval and cannot be issued here. Tell the user to ask a manager to approve the refund of ${header.amt} on order ${header.orderId} in the back office." - simple: "${header.daysSince} > 30 && ${header.damagedOrDefective} != true" steps: - setHeader: name: CamelAiToolIsError constant: true - setBody: simple: "Order ${header.orderId} was delivered ${header.daysSince} days ago, outside the 30-day refund window. Only damaged or defective items can be refunded after 30 days (policy://refunds); otherwise offer store credit (issue_store_credit, needs a manager) or a repair." otherwise: steps: - to: "sql:insert into refunds (order_id, amount, reason, created) values (:#orderId, :#amt, :#reason, '{{acme.today}}') returning id?dataSource=jdbc:rustsql:mem:acme&outputType=SelectOne" - setHeader: name: refundId simple: "RF-${body}" - to: "sql:update orders set refunded = refunded + :#amt where id = :#orderId?dataSource=jdbc:rustsql:mem:acme" - setBody: simple: '{"refundId": "${header.refundId}", "orderId": ${header.orderId}, "amount": ${header.amt}, "status": "refunded to the card on file, 3-5 working days"}' ``` - **The amount comes from the order.** Without `amount` the route refunds what has not been refunded yet; with it, it must be more than 0 and at most that. - **The model cannot talk its way past a rule.** The prompt and the policy document help the model explain; the `choice` in the route decides. - **Refusals are results, not exceptions.** An exception would reach the client as a generic "Tool issue_refund failed" (errors are hidden by default); `CamelAiToolIsError` with a sentence gives the model something to tell the user. - **The policy is also a document** (`policy://refunds`), so Claude can quote it; see [prompts and resources](prompts-and-resources.md). ## Try it Run the shop, connect a client, and ask for the refunds above. `shop_use_cases` in `crates/cameleer-main/tests/mcp_shop.rs` runs each rule over MCP: outside the window, over the limit, one line of an order, a full refund, and a second refund of the same order. ## Related - [Actions guarded by approvals](approvals.md), [A manager in the loop](manager-approval.md) - [Direct tool calls vs Cameleer](../agent-tool-calls.md): the same idea across four systems with a saga ## Found a problem? If something on this page doesn't match what Cameleer does, please [open an issue](https://github.com/pmsudhi/cameleer/issues/new), or fork the repository, fix it, add a test, run `cargo test --workspace` and open a pull request.