The four-tool moat
Tonight I shipped a Density Altitude calculator. That makes four free tools on tarmaclabs.org: METAR, Currency, Weight & Balance, and now DA. Four is a number that matters. Here's why.
Four free tools live at tarmaclabs.org/tools as of tonight. METAR decoder, 14 CFR Part 61 currency calculator, universal weight & balance, and now density altitude.
One tool is a freebie. Two tools is a lead magnet. Three tools is a marketing decision. Four tools is a moat.
What "moat" means here
The free-tool playbook isn't new. Plenty of aviation software companies ship a calculator or two as SEO bait. Type "density altitude calculator" into Google and you'll find half a dozen sites that exist solely to rank for that one keyword and route to a signup form. They're technically free. They're technically calculators. They're also full of trackers and signup walls and "register to see results" nonsense.
A four-tool moat is different. When a CFI lands on the currency calculator and the math is right and there's no signup wall, and then they notice the link to the W&B calculator that respects their POH numbers, and then the METAR decoder, and then the DA calc — that's when something shifts in their head. This isn't one calculator. This is a small company that ships engineering, full stop.
One tool is a freebie. Two is a lead magnet. Three is a marketing decision. Four is a moat.
Why four specifically
Four is the count where the page stops looking like an afterthought and starts looking like a section of a real company. A `/tools` page with 1 link is sad. With 2 is incomplete. With 3 is "getting there." With 4 in a clean grid, with an "Endorsement Lookup — coming soon" in the fifth slot to show momentum, the page reads like a product surface.
Plus: four tools means four chances per visitor to find one they need that week. A CFI might not care about W&B today (they're flying a familiar 172) but very much cares about density altitude when they fly to a 5000ft field in July. The bigger the surface area of utility, the higher the probability a given visitor walks away thinking TarmacLabs is a company I'll come back to.
The cost of the fourth tool
About 45 minutes including this post. The DA calc is ~200 lines of TypeScript: parse inputs, run the pilot rule-of-thumb formulas (PA via altimeter offset, DA via 120ft per °C above ISA), produce a verdict band, optionally compute relative humidity from dewpoint for an advisory, render the result panel.
The reason it's 45 minutes and not 45 days is that the pattern is already locked. W&B taught me the shape. Currency taught me the trust-via-correctness angle. By the fourth one, the only real work is the domain math — the UI, the testing, the styling, the SEO metadata are all just filling in a template.
Where this is going
Each free tool is built on the same engineering convictions as the paid products. The DA calculator uses the same kind of pure-function rule engine that drives AutoBrief's GO/NO-GO. The currency calc respects the same end-of-month conventions Trim uses for endorsement expiration. The W&B doesn't ship hardcoded aircraft data — same rule that AutoBrief enforces about FAA reference data.
So when a chief pilot eventually pays for AutoBrief, they're not signing up for a black box. They've already used four pieces of software built by the same person, on the same principles, with the same level of care. The moat isn't the four tools. The moat is what the four tools prove about everything else we ship.