API Tool Calls

Fuel Cost Calculator

fuel_cost

Read-onlyIdempotent

Calculate trip fuel quantity and cost from entered distance, fuel economy, fuel price and currency; supports US mpg, L/100 km and km/L.

Example tool call

This call uses example arguments supplied in the tool’s input schema.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "price": 4,
      "units": "us_mpg",
      "economy": 30,
      "currency": "USD",
      "distance": 300
    },
    "name": "fuel_cost"
  }
}

Input Schema

Name	Required	Description
`price`	Yes	Entered price per US liquid gallon for us_mpg, per liter otherwise.
`units`	Yes	Unit system; Imperial mpg not accepted.
`economy`	Yes	Positive US mpg, L/100 km or km/L as selected.
`currency`	Yes	Entered three-letter currency label (letters only), shared by all prices; no exchange rates.
`distance`	Yes	Nonnegative miles for us_mpg; kilometers otherwise.

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

AddedOct 4, 2026

TDQS

A3.9/5.0

Behavior3/5

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds nothing behavioral beyond that — no note that this is a pure offline arithmetic computation with no external data or rate lookups (that detail sits in the schema's currency field instead).

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?

A single well-formed sentence that front-loads the core action and appends the supported unit systems. Every clause earns its place with no redundancy.

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

Completeness5/5

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

For a deterministic, stateless arithmetic tool with full annotation coverage, a complete output schema, and 100% schema description coverage, the description supplies everything needed to invoke it correctly. Return values need not be explained since an output schema exists.

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 all five parameters (including the units enum and the conditional mile-vs-kilometer semantics) are already documented in the schema. The description restates the parameter list without adding syntax, defaults, or edge-case guidance 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 ('Calculate trip fuel quantity and cost') and enumerates the exact inputs it consumes (distance, fuel economy, price, currency). The supported unit systems (US mpg, L/100 km, km/L) make it clearly distinct from generic siblings like unit_convert or unit_price.

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

Usage Guidelines3/5

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

Usage is implied by the narrow purpose — an agent can infer this is the tool for fuel cost estimation — but the description names no alternatives and gives no explicit when-to-use or when-not-to-use guidance. The only exclusion ('Imperial mpg not accepted') lives in the schema, not the description.

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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