S&P 500 / US30 Market Compass — A free desktop app from Algomist

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The core problem it solves: Headline index numbers can lie to you. "The S&P 500 is up 0.4%" might mean broad, healthy participation across hundreds of stocks — or it might mean 5 mega-cap names ripped higher while 300 stocks were red. The index number alone can't tell you which. This app can.

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What it does:

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• Pulls live price data for either the S&P 500 or the Dow Jones (US30), for any date/time you specify

• Calculates two different averages side by side:

  • Simple average — the plain, unweighted average % change across every stock, a pure read on breadth

  • Weighted average — calculated using each index's actual official methodology: cap-weighted for the S&P 500 (bigger companies move the index more), price-weighted for the Dow (higher-priced stocks move it more)

• Shows market breadth — how many stocks advanced vs. declined vs. were flat

• Flags divergence automatically — when the weighted average and breadth point in opposite directions, it surfaces a plain-language warning telling you a handful of stocks are likely masking the broader move

• Displays a top-10 table of the stocks carrying the most weight in that day's move, so you can see exactly who's responsible

• Logs every snapshot to CSV, building a historical record over time

 

Why it matters for traders: A rally driven by 5 stocks behaves very differently — and carries very different risk — than one with genuine broad participation. This tool turns that invisible distinction into a number you can see in seconds, instead of digging through individual stock charts or guessing from the headline.

The experience: Clean, dark trading-terminal interface (matching the rest of the Algomist toolset), one-click snapshot generation, live progress feedback while it pulls data, and results you can read at a glance — no spreadsheet required.