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splitwise-mcp

by chrischall
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Remote

sw_create_expense

Destructive

Create a Splitwise expense. Use split_equally:true to split evenly among group members, or provide a users array for custom per-person splits (paid_share and owed_share as decimal strings like "25.00"). cost must be a decimal string.

Instructions

Create a Splitwise expense. Use split_equally:true to split evenly among group members, or provide a users array for custom per-person splits (paid_share and owed_share as decimal strings like "25.00"). cost must be a decimal string. Pass receipt to attach an image or PDF in the same call. This puts charges on every participant's balance and notifies them. Asks the user to confirm first: a confirmation prompt where the client supports one; otherwise the first call returns a preview and a confirmToken, and only a repeat call with that token proceeds (see MCP_CONFIRM_MODE).

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
costYesTotal cost as decimal string, e.g. "25.00"
dateNoISO 8601 datetime
usersNoCustom split (mutually exclusive with split_equally). Full list of participants required.
detailsNoNotes
receiptNoReceipt to attach: PNG, JPEG, GIF or PDF, up to 10 MiB. Give exactly one of base64 or path. The type is detected from the file contents. Replaces any receipt already on the expense.
group_idYesGroup to add expense to (use 0 for no group)
category_idNoCategory id from sw_get_categories
descriptionYesShort description of the expense
confirmTokenNoONLY for the two-step confirmation fallback (a client without MCP elicitation). The confirmToken from this same tool's phase-1 "confirmation-required" response, passed back ONLY after the user has seen that preview and explicitly approved it in chat — never on the first call, never invented, never reused. Call again with the same arguments. Ignored when the client supports elicitation.
currency_codeNoCurrency code, e.g. "USD". Defaults to group/user default.
split_equallyNoSplit equally among group members (mutually exclusive with users)

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv3.4.0
    • addedInput schema / properties / receipt
      Added value: +{
+  "description": "Receipt to attach: PNG, JPEG, GIF or PDF, up to 10 MiB. Give exactly one of base64 or path. The type is detected from the file contents. Replaces any receipt already on the expense.",
+  "properties": {
+    "base64": {
+      "description": "The file bytes, base64-encoded (a data: URL prefix is accepted and stripped). The normal way to pass a receipt.",
+      "minLength": 1,
+      "type": "string"
+    },
+    "filename": {
+      "description": "Name to store the file under, e.g. \"receipt.pdf\".",
+      "maxLength": 200,
+      "minLength": 1,
+      "type": "string"
+    },
+    "mime_type": {
+      "description": "Optional. If given, it must match the type detected from the file contents.",
+      "type": "string"
+    },
+    "path": {
+      "description": "A file inside SPLITWISE_INPUT_DIR on the machine running this server (relative to it, or absolute). Only works when that variable is set — never on a hosted server; use base64 there.",
+      "minLength": 1,
+      "type": "string"
+    }
+  },
+  "required": [
+    "filename"
+  ],
+  "type": "object"
+}
  2. Changed2 schema fields changedv3.2.0
    • removedInput schema / properties / confirm
      Removed value: -{
-  "description": "Must be true to proceed. Without this, the tool returns a preview.",
-  "type": "boolean"
-}
    • addedInput schema / properties / confirmToken
      Added value: +{
+  "description": "ONLY for the two-step confirmation fallback (a client without MCP elicitation). The confirmToken from this same tool's phase-1 \"confirmation-required\" response, passed back ONLY after the user has seen that preview and explicitly approved it in chat — never on the first call, never invented, never reused. Call again with the same arguments. Ignored when the client supports elicitation.",
+  "type": "string"
+}
  3. Changed1 schema field changedv3.0.0
    • changedInput schema / $schema
      Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"
  4. First observedv2.1.5

TDQS

A4.2/5.0
Behavior5/5

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

Annotations only flag readOnly=false, destructive=true, openWorld=true; the description goes well beyond them by disclosing the actual side effects ('puts charges on every participant's balance and notifies them') and the entire two-phase confirmation protocol including the preview/confirmToken fallback and the MCP_CONFIRM_MODE reference. That is exactly the kind of impact disclosure a mutation tool needs.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Single paragraph, front-loaded with the core action before the split mechanics, side effects, and confirmation protocol. The confirmation sentence is long but carries non-redundant information; nearly every clause earns its place, though the paragraph could be split for scanability.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For an 11-parameter tool with nested objects and no output schema, the description covers split logic, receipt attachment, side effects, and the confirmation handshake well. It never states what a successful (non-confirmation) call returns, but everything needed to invoke it correctly is present.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

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 interaction-level meaning the schema cannot: the paid_share/owed_share decimal-string convention tied to custom splits, the receipt-in-same-call option, and the fact that confirmToken is only valid on a repeat call after approval. These clarify how parameters combine into a workflow rather than just restating field docs.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The opening sentence 'Create a Splitwise expense' gives an unambiguous verb+resource, and the split-mode and receipt details make the tool's remit concrete. Sibling differentiation is only implicit (attaching a receipt 'in the same call' implicitly contrasts with sw_attach_receipt, and 'create' contrasts with sw_update_expense), but no sibling is named, so it stops short of a 5.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It clearly states the branch conditions for the two split modes ('use split_equally:true ... or provide a users array') and thoroughly explains when each confirmation path applies. It does not route the agent away from any alternative tool by name, so it lacks the explicit exclusions a 5 requires.

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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