Eratsuku

Overview

Eratsuku helps you decide how to build a website before you start. Answer eight questions and it scores nine approaches — WordPress, no-code builders, e-commerce platforms, custom development, and hiring an agency — on the same axes, then shows the fit, the reasoning behind it, the likely cost, and what to do next. It is written for small businesses, shops, professional practices, and sole proprietors, on the assumption that the reader is not a web specialist. Development started on 2026-07-31 and the product is still pre-launch.

The problem

Comparisons of website-building options tend to be either vendor marketing or generic advice with the conditions stripped out. Prices circulate as ballpark figures with no source, so the assumptions only surface after the contract is signed. Even services that call themselves diagnostics can return different results for the same answers, and give the user no way to check whether affiliates are being pushed to the top.

Key features

• Eight questions, scoring nine approaches across seven axes: purpose, budget, features, update frequency, who updates, maintenance, and launch timing
• Ranking and fit are computed deterministically — no randomness, no current time — so the same answers always give the same result
• Affiliate data is isolated from the scoring code, and a test checks that the scoring side never imports it
• Every price is a quotation from a saved copy of the vendor's own pricing page; the check fails if that exact string isn't there
• Approaches that cannot meet a stated condition are kept out of the top spots, with the unmet condition shown as the reason
• For approaches with no published pricing, no ballpark figure is invented — it is shown as requiring a quote
• A pricing simulator that switches between setup cost, monthly cost, and 1 / 3 / 5-year totals
• Answers are never sent to a server; the diagnosis runs entirely in the browser

Tech stack

Architecture

A static Next.js 16 App Router export served from S3 + CloudFront, with no backend. The diagnosis runs entirely in the browser and answers never reach a server. The one exception is the enquiry form, which posts to a separate Lambda Function URL and arrives by SES. The scoring logic and the build-method data depend on neither React nor Next.js, so tests read them straight from Node. CSP and security headers live in a single JSON file that both the CDK stack and the local strict server read, so the two cannot drift. Infrastructure is three AWS CDK stacks — site, CI/CD, and form — and the domain eratsuku.jp stays with Sakura Internet, pointing its DNS at CloudFront.

AI's role and boundaries

The brand carries "AI" in its name, but no LLM takes part in computing the ranking or the fit score. The comparison rests on the same answers always producing the same result, and the page states outright that the explanations are not AI-generated. Only the explanation text is factored out behind a replaceable interface, so handing it to an LLM later would still leave the ranking logic untouched. AI works on the production side — implementation, article structure, and review. Remove it and the ranking is unchanged; quality rests on 28 unit tests over the scoring logic and a string-for-string match of every published price against the saved vendor page.

Evaluation & Operations

The site is pre-launch, so there is no traffic yet. The bar is that no one signs a contract based on a wrong number. Every published price is matched string-for-string against the saved vendor page, and the check fails on any mismatch. Some vendors render prices in JavaScript, so the pages are captured with Playwright rather than fetched raw. The scoring logic has 28 unit tests, and seven gates run before every push: types, lint, source matching, text contrast, unit tests, build, and browser checks. After launch, "the deploy succeeded" and "the fix is live" are verified separately, by checking every sitemap URL and the security headers against production.