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rail-mcp

rail-mcp

by tstockham96
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

Set budget

set_budget
Idempotent

Overwrite the local spend budget ledger limit for agent purchases. Set amount in USD; it only changes the limit and does not spend, approve cards, or settle purchases.

Instructions

Overwrite the local spend budget. Changes the ledger limit only. Does not spend money, approve a card, settle a purchase, or contact Stripe or Link. Passing the same amount again does not add to the budget.

Tool call template

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": {
      "amount_usd": "<amount_usd>"
    },
    "name": "set_budget"
  }
}

Input Schema

NameRequiredDescriptionDefault
noteNoOptional note for this budget
currencyNoCurrency code; default USD
amount_usdYesBudget amount in USD

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.1

TDQS

A4.2/5.0
Behavior4/5

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

Annotations already declare idempotentHint=true and openWorldHint=false, so the description's job is to add nuance. It does so usefully: 'Passing the same amount again does not add to the budget' clarifies that idempotency here means overwrite rather than increment, and 'Changes the ledger limit only' scopes the blast radius. It omits any permission or auth requirements, keeping it below 5.

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?

Three short sentences, front-loaded with the action and effect, then the exclusions and the idempotency caveat. Every sentence carries distinct information with no redundancy.

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 three-parameter mutation with no output schema and annotations covering the safety profile, the description covers what the tool changes, what it does not change, and repeat-call behavior. It lacks any statement of required permissions or the resulting state after the overwrite, which keeps it from a 5.

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 100%, so amount_usd, currency, and note are already documented in the schema; the baseline of 3 applies. The description adds no format, range, or unit detail beyond what the schema provides.

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?

States a specific verb and resource ('Overwrite the local spend budget') plus the precise effect ('Changes the ledger limit only'). It is clearly distinguishable from siblings like propose_purchase and refund_receipt, which the description explicitly disclaims.

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 negation list ('Does not spend money, approve a card, settle a purchase, or contact Stripe or Link') effectively tells the agent when this tool is not the right one, which is strong routing guidance. It stops short of naming the sibling tool an agent should use instead, so it is not a full 5.

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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