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Gas Prices Today MCP

by io.github.theluckystrike
OverviewDiscussionsAdmin

Estimate fill-up and trip cost

estimate_fill_up_cost
Read-onlyIdempotent

Cost of filling a tank (gallons times this week's EIA average for the area, or your price per gallon), and optionally the fuel cost of a trip from miles and miles per gallon, including cents per mile.

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": {
      "gallons": "<gallons>"
    },
    "name": "estimate_fill_up_cost"
  }
}

Input Schema

NameRequiredDescriptionDefault
areaNoUS, a state name or code ("Texas", "CA"), a city EIA prices ("Chicago", "NYC"), or an EIA region ("Midwest", "PADD 2"). Default US. A state EIA does not price is answered with its region.
gradeNoDefault regular.
milesNoTrip distance in miles. Give with miles_per_gallon.
gallonsYesGallons to buy, for example 15.
miles_per_gallonNoYour vehicle fuel economy. Give with miles.
price_per_gallonNoYour own price per gallon. Default the EIA average for the area.

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observed

TDQS

A3.8/5.0
Behavior4/5

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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds real substance beyond them: it discloses the data source (this week's EIA average for the area) and the output semantics (cost, and cents per mile). It does not disclose the fallback behavior for states without EIA pricing, which is a minor gap.

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?

A single dense sentence with the primary tank-fill purpose front-loaded before the optional trip extension. It is slightly run-on with nested parentheticals, but every clause carries information and nothing is padded.

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?

With no output schema, the description must hint at return values, and it does so by naming the cost and cents-per-mile outputs. Six parameters with full schema coverage are already explained in the schema, and the annotations cover the safety and world-access profile, so nothing material is missing.

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% and each parameter already documents defaults, ranges and pairing constraints, so the schema carries the load. The description reinforces the area-price versus custom price_per_gallon choice and the miles/miles_per_gallon pairing but adds no new format or edge-case guidance. Baseline 3 is appropriate.

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 description names a specific computation (tank fill cost) and its formula components (gallons times this week's EIA average, or your price per gallon), plus the optional trip-cost extension with cents per mile. It does not distinguish itself from the sibling price-lookup tools, so it falls 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 Guidelines3/5

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

Usage is only implied: an agent can infer this is the calculator rather than the price fetchers, since siblings compare_gas_prices and get_gas_prices are named in the tool list but never referenced here. There is no explicit when-to-use, when-not-to-use, or routing statement, and no mention that trip cost requires miles together with miles per gallon beyond what the schema already says.

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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