Wattoku MCP server documentation
Wattoku is an MCP server for comparing and estimating household utility costs in Japan. Connect it to an AI assistant and the whole path — from an annual cost estimate to a sign-up link — happens inside the conversation. No authentication is required; adding the URL is enough.
- Endpoint:
https://wattoku.meliorra.co/api/mcp(Streamable HTTP) - Areas covered: Hokkaido, Tohoku, Tokyo, Chubu, Hokuriku, Kansai, Chugoku, Shikoku, Kyushu and Okinawa
- Data: built from each company's official published tariffs as the primary source, with a source URL and a verification date attached to every figure. Fuel-cost adjustment is updated monthly and the renewable energy levy annually
- Language: the service covers Japanese utilities, and tool responses are written in Japanese
Using it from Claude.ai
- Open Settings → Connectors → Add custom connector in Claude.ai (paid plan)
- Enter a name (for example Wattoku) and the remote MCP server URL
https://wattoku.meliorra.co/api/mcp, leaving authentication set to none - Ask about electricity, gas, fiber or mobile costs in the chat
Using it from Claude Code
claude mcp add --transport http wattoku https://wattoku.meliorra.co/api/mcpUsing it from ChatGPT (developer mode)
- Turn on Developer mode under Settings → Apps & Connectors → Advanced settings (Plus / Pro / Business)
- Choose Create, enter a name and the MCP server URL
https://wattoku.meliorra.co/api/mcp, select “No authentication” and save - Pick the connector from the “+” menu in a chat
Electricity tools, with examples
search_plans — Search household electricity plans
Searches household electricity plans from the supply area, contract ampere and household size (or monthly kWh), each with an annual cost estimate. Results are sorted cheapest first. Set green_only to see only plans whose provider states, at no extra cost, that the electricity is effectively 100% renewable with net-zero CO2.
Example: “I'm a family of four in Kansai. Which electricity plan should we be on?”
Returns: The plans we carry for that area, cheapest annual estimate first, with a volatility warning attached to market-linked plans.
simulate_cost — Annual estimate and comparison with the current contract
Estimates each plan's annual cost — and the difference against the current contract — from monthly kWh, or by working backwards from the current monthly bill. The annual figure is a 12-month build-up that accounts for seasonal variation.
Example: “I live alone in Tokyo and pay about ¥7,000 a month. Can I do better?”
Returns: Usage inferred from the bill (stating the assumed plan and ampere) and the annual difference against the assumed current contract. If switching would not pay, it says so.
compare_plans — Detailed comparison of electricity plans
Compares two to five plans including the annual estimate, cancellation fees, how fuel-cost adjustment works (capped or not), loyalty points and bundle discounts.
Example: “The first and third plans — how do their cancellation fees and fuel adjustments differ?”
Returns: Strengths and caveats side by side (cancellation fees, uncapped fuel adjustment, market-linked risk and so on).
get_switch_link — Issue a sign-up link
Issues a link to the sign-up page for the plan you chose. You complete the application yourself on the retailer's own site — we neither broker nor act as an agent.
Example: “Give me the sign-up link for the cheapest plan.”
Returns: A checklist of what to have ready (such as the supply point identification number), plus a disclosure, on every call, that the link may be an affiliate link.
Fiber internet tools, with examples
Fiber plans are compared on what they effectively cost once the cashback conditions are taken into account, not on the headline cashback. The expected value is our own estimate, not a measured claim rate, and the basis for it is included in every response.
search_hikari_plans — Search fiber internet plans
Searches fiber plans by building type (house or apartment), mobile carrier and number of lines, sorted by effective total cost (monthly fees + setup fee + construction cost − cashback). Alongside the headline cashback it shows an expected value derived from how the cashback must be claimed, how long the wait is and when the claim window closes, together with the total if the cashback is never received.
Example: “We're in an apartment, on au, three lines in the family. Which fiber plan?”
Returns: Candidates by effective total, each with the cashback conditions, the real cost of any add-on required for a bundle discount, and the cost of cancelling. Ranking uses headline figures only — our expected values never move the order.
simulate_hikari_cost — Effective total cost of one fiber plan
Breaks the effective total down month by month, returning three totals — cashback received as advertised, expected value, and cashback never received — along with the full set of assumptions.
Example: “Redo the first one over 60 months.”
Returns: A monthly breakdown (base fee, construction instalments, monthly credits, required add-ons, bundle discounts), the three totals, and the cost of cancelling early.
compare_hikari_plans — Detailed comparison of fiber plans
Compares two to five plans including cashback conditions, cancellation fees, removal fees, remaining construction instalments and bundle discounts.
Example: “Compare the first two, including how easy the cashback is to actually claim.”
Returns: A table that makes the underlying trade-off visible: a large headline cashback can lose on expected value when the claim conditions are harsh.
switch_hikari_cost — Total cost of switching fiber providers
Takes the cost of leaving your current contract (cancellation fee, remaining construction instalments, removal fee) and its monthly price, and returns the difference between switching and staying. If staying is cheaper, it says so.
Example: “I'm on Docomo Hikari at ¥5,720 a month with a ¥5,500 cancellation fee. Worth switching?”
Returns: The difference in total cost including the cost of switching, plus the difference if the cashback is never received.
Every tool except get_switch_link is read-only. get_switch_link creates one internal short-link record the first time it is called for a plan. No tool creates, changes or deletes any of your data.
City gas tools, with examples
search_gas_plans — Search city gas plans
Returns gas plans for a supply region (the Tokyo Gas, Osaka Gas or Toho Gas area) and household size, cheapest annual cost first. Because gas tariffs switch both the standing charge and the unit rate by usage band, and usage is concentrated in winter, the comparison is a 12-month build-up with seasonal variation.
Example: “Two of us in Osaka — can we cut the gas bill?”
Returns: Cheapest annual estimates, plus the January monthly figure, the month of the raw-material cost adjustment applied, and the source.
simulate_energy_bundle — Combined electricity + gas estimate
Maps the gas supply region to the matching electricity area and returns the combined annual cost of the cheapest plan on each side. Bundle discounts are disclosed as a note rather than folded into the total, because their conditions differ from plan to plan.
Example: “Family of three in Tokyo. How much would we save reviewing electricity and gas together?”
Returns: The combined total for the cheapest pairing, plus the individual rankings.
Mobile tools, with examples
search_mobile_plans — Search mobile plans
Returns mobile plans for a monthly data allowance (or unlimited), cheapest monthly price first. Prices are tax-inclusive and unconditional — family discounts and fiber bundle discounts are reported separately, with their conditions and amounts.
Example: “I use about 20 GB a month. What's the cheapest carrier?”
Returns: Cheapest monthly price first, with each plan's allowance, whether calls are included, any conditional discounts, and the source.
Troubleshooting
- “No standing charge for that contract capacity” — some plans are limited to certain ampere ratings (Chubu Electric's Otoku plan, for example, starts at 40 A). Retry with a different contract_ampere.
- Working backwards from a bill fails — the bill cannot be reversed if it is below the standing charge. The error includes the minimum, so retry with a larger amount or give the kWh from your meter reading slip.
- No ampere question in Kansai, Chugoku, Shikoku or Okinawa — those areas use a minimum-charge system with no contract ampere, so nothing needs to be specified. This is expected behaviour.
- A market-linked estimate differs from the real bill — market-linked plans reprice every 30 minutes, so the estimate is an approximation based on recent market results.
Data and neutrality
Search, estimate and comparison results are ordered by annual cost calculated from the tariff data, and by nothing else. We take part in affiliate programs, but whether a plan pays a commission — and how much — never affects its ranking or whether it is recommended. See our disclaimer and advertising notice and FAQ (both in Japanese).