How Arithmos works
From a one-sentence prompt to a transparent, rules-based index with holdings, rationale, and a 10-year backtest, ready to export to any broker. Under a minute. No code required.
- 01start here
Describe the index
One sentence in plain English. The 20 largest US semis weighted by revenue growth, debt-to-equity capped at 2.
step-1read → - 02
Watch it screen
The agent parses the rules, pulls the live universe, and applies the filters in front of you. Each step is logged.
step-2read → - 03
Audit the holdings
Tickers, weights, the rule the agent compiled, the universe it screened. Every cell shows its working.
step-3read → - 04
Read the backtest
Ten-year, daily-rebalanced, against actual prices. Equity curve vs the S&P, plus Sharpe, CAGR, and max drawdown.
step-4read → - 05
Export or publish
Hand the basket to your broker as CSV, JSON, Trading 212 Pie, or Fidelity Basket. Or publish it for others to fork.
step-5read →
- step 1prompt
- step 2screen
- step 3rules
- step 4backtest
- step 5export
Describe the index in plain English
Arithmos starts with one text box. Type the exposure you want in a single sentence and the agent parses it into formal rules.
The more specific the prompt, the more specific the index. Mention the universe, the filters, the weighting, and any caps you care about.
Watch the agent screen the universe
Arithmos parses your prompt into a rule set, fetches the live universe of equities and ETFs, and applies your filters in real time. You see each step as it happens: universe, filter, weighting, cap.
Data comes from Financial Modeling Prep, Tiingo, Finnhub, and others. Failures show up inline. Nothing is silently fudged.
Review the holdings and the rules
The result is a transparent index. A holdings table with weights, the explicit rule set the agent compiled, a written rationale, and the exact universe and filters used. Every cell is auditable.
Hover any metric for a plain-English explanation. Arithmos doesn't hide jargon.
| ticker | name | weight |
|---|---|---|
| NVDA | NVIDIA Corp | 18.4% |
| AVGO | Broadcom Inc | 12.1% |
| AMD | Advanced Micro Devices | 9.7% |
| TSM | Taiwan Semiconductor | 8.3% |
| ASML | ASML Holding | 6.9% |
| MU | Micron Technology | 5.4% |
Read the 10-year backtest
Arithmos runs a daily-rebalanced backtest against actual historical prices and shows the equity curve vs the S&P 500, plus Sharpe, Sortino, CAGR, volatility, and max drawdown.
See /backtest-methodology for the full procedure including survivorship-bias handling.
Export to your broker, or share publicly
Export the holdings as universal CSV, JSON, or plain text, or in broker-specific formats like Trading 212 Pie and Fidelity Basket. Arithmos is platform-agnostic by design. It gives you the rules; you execute the trades.
Or publish the index to your public profile so other users can build on top of it. Your prompt and the rationale travel with the index.
Common questions
What is Arithmos?
Arithmos is an AI-powered custom index builder. You describe the exposure you want in plain English; Arithmos returns a transparent, rules-based index with holdings, rationale, and a 10-year backtest. It is a research and data tool, not a regulated broker or investment advisor.
How long does it take to build an index?
Most prompts produce a finished index with a 10-year backtest in under a minute. Larger universes and tighter filters take a little longer; you see live progress as the agent works.
Can I see exactly how Arithmos picked the holdings?
Yes. Every index ships with the formal rule set the agent compiled from your prompt, the universe it screened, the filters it applied, the weighting method, and the per-holding rationale. There is no opaque scoring layer.
How accurate are the backtests?
Backtests are computed against actual historical end-of-day prices using a daily-rebalanced simulation. Survivorship bias is documented in /backtest-methodology. Past performance is not a guarantee of future results.
Can Arithmos place trades for me?
No. Arithmos is platform-agnostic by design: it produces the holdings and weights, and you execute through your own broker. We export universal CSV, JSON, and plain text, plus broker-specific formats like Trading 212 Pie and Fidelity Basket.
Is Arithmos investment advice?
No. Arithmos is a research and data tool. Nothing on the platform constitutes investment advice, and Arithmos is not a regulated broker or financial advisor. Talk to a licensed advisor before making investment decisions.
Do I need to know how to code?
No. Arithmos takes plain-English prompts. The interface is a single text box; the rules, holdings, and backtest are produced for you.
Try it with your own prompt
Browse every public index and run full backtests for free. Building your own starts on Plus — see /pricing for plans.
build an index →