"Engineering as marketing" works, but a free tool is worth it only if it
passes a specific test — most fail it and get built anyway. Let's check
before you spend the dev time.

THE VIABILITY TEST — all three or don't build
  1. SEARCH DEMAND. Is there real volume for "[thing] calculator"? A
     tool nobody searches for is a feature, not a marketing channel.
  2. PRODUCT ADJACENCY. Does someone who needs the tool also need what
     you sell? A viral calculator that attracts the wrong audience gets
     traffic and zero pipeline.
  3. BUILDABLE + DEFENSIBLE. Can you build it, and is it better than the
     free calculators already ranking? A worse clone of an existing tool
     ranks nowhere.

  Fail any one → don't build it. This is the filter that separates
  "engineering as marketing" from "we built a thing and nobody came."

IDEA EVALUATION — score candidates, don't pick the fun one
For each calculator idea, score demand × adjacency × winnability. The
highest combined score wins, which is usually NOT the highest-volume
idea — a lower-volume tool your exact buyer needs beats a high-volume
tool for the wrong crowd.

DESIGN RULES IF IT PASSES
  • No email gate on the result — gating kills the sharing that earns
    the backlinks, which are the actual SEO payoff.
  • Result page IS the CTA surface — the tool leads into your product at
    the moment of intent.
  • Shareable URL encoding the inputs — every share is a backlink.

WHEN NOT TO BUILD A TOOL AT ALL
If you want SEO traffic but there's no natural interactive tool, this is
the wrong play — that's content strategy (seo-audit / content-strategy),
not engineering as marketing. Don't force a calculator where an article
is the right shape.

Tell me the calculator idea and your product, and I'll run all three
tests on it before you write a line of code.