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splitwise-mcp

by chrischall
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Remote

sw_update_expense

Update an existing Splitwise expense: provide the expense ID and any fields to change. For custom splits, include the full users array to replace the split.

Instructions

Edit an existing Splitwise expense. Provide expense_id and any fields to change. For custom split updates, the full users array must be provided (the API replaces the entire split). 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
costNoDecimal string, e.g. "25.00"
dateNo
usersNoFull replacement split — all users must be included. Mutually exclusive with split_equally.
detailsNo
expense_idYesID of the expense to update
category_idNo
descriptionNo
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_codeNo
split_equallyNoMutually exclusive with users

Schema Changelog

Changes observed during successful MCP inspections.

  1. 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"
+}
  2. 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"
  3. First observedv2.1.5

TDQS

A4.2/5.0
Behavior4/5

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

With no annotations provided, the description carries the full behavioral burden. It discloses the confirmation prompt behavior, the preview/confirmToken fallback, and the fact that the API replaces the entire custom split rather than merging changes. This is substantial, though it does not discuss permission requirements or reversibility beyond the implied edit operation.

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

Conciseness5/5

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

The description is dense but every sentence adds essential information: the basic edit action, the split-replacement caveat, and the confirmation flow. It is front-loaded with the primary purpose and contains no filler.

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 a 10-parameter mutation tool with no annotations and no output schema, the description covers the key invocation hazards: required expense_id, full users array replacement, and the two-step confirmation protocol. It does not explain the success response shape of the final call, but the confirmation/preview flow is sufficiently described for an agent to call the tool correctly.

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

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is only 50%, so the description needed to compensate for undocumented parameters. It does explain the critical semantics of users (full replacement array) and confirmToken (only on repeat calls after approval), but other parameters like date, details, category_id, and currency_code receive no added meaning beyond their names. The description is adequate but leaves clear gaps.

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

Purpose5/5

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

The description opens with a specific verb and resource: 'Edit an existing Splitwise expense.' It clearly distinguishes editing from the sibling create/delete/undelete expense tools and tells the agent exactly what action this tool performs.

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?

The description states to provide expense_id and any fields to change, and gives specific conditions for custom split updates and two-step confirmation. It does not explicitly name alternatives like sw_create_expense or sw_delete_expense, but the 'existing expense' framing plus sibling names makes the appropriate context clear.

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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