Composer

What it is

Composer is a hosted, no-code builder for rule-based equity strategies. You assemble a "symphony" out of blocks — assets, weights, conditionals, filters, groups — backtest it, and hand it to Composer's own brokerage to rebalance on a schedule without you touching it. That last step is the unusual part: most tools in this category stop at a signal, and Composer routes the order itself, through Composer Securities LLC with Alpaca and Apex clearing behind it. SoFi acquired the company in June 2026 and the product carries on unchanged.

An AI assistant turns a plain-English description into a symphony you then edit, and Discover surfaces strategies from a library of more than 2,000 that other users built. Both produce an editable rule set rather than a pick, and nothing trades until you invest in it.

Pricing

What the free tier withholds is narrower than it looks: the editor, backtests, watching a strategy forward, the AI and the API are all free, and so is placing your own stock and ETF trades. Only automated strategy execution is paid, along with unlimited backtesting and retirement accounts. The Trading Pass costs $40/month month-to-month or $384 a year ($32/month) — and the backtester will model that subscription as a cost if you ask it to, which is fairer than most, though it is off by default.

Stock and ETF trades carry no commission, only pass-through SEC and FINRA fees; options are $0.65 per contract plus $5.00 per position exercised or assigned. The deposit minimum is $50 and each symphony needs $50, though Composer recommends $2,500 across the portfolio to avoid unfilled orders, since not every asset is fractionable.

Data & coverage

US stocks, ETFs and listed options. Quotes come from Xignite and Polygon, and the options chain is live. Backtests are a different animal: daily adjusted closing prices, a default slippage assumption of 1 basis point, and a date picker that reaches back 30 years.

Crypto is gone — support ended 31 January 2026 and remaining positions were liquidated on 4 February. Crypto ETFs are unaffected.

Integrations

A REST API issues a key and secret and covers accounts, portfolio statistics, symphonies, backtests, direct trading and CSV activity reports. Limits are per key and per endpoint, per minute: most endpoints allow 25 requests a minute, and a handful of symphony and portfolio endpoints are raised to 100, 250 or 500 — the 500 belongs to the per-symphony portfolio statistics call, not to backtesting.

There is also a first-party MCP server, so an LLM client can build and backtest symphonies and, with a key, read and trade an account. It is published as the composer-trade-mcp package and runs locally against the same REST API; the backtesting tools work without an account at all. It is no longer maintained in the open, though — see Limitations.

A help-centre article still says Composer supports no integrations with external apps or platforms, but it was last touched in June 2025, before either the documented API or the MCP server, and it is best read as being about consumer app connections rather than the developer surface.

Limitations

• US residents only, for building and watching as well as trading.
• Backtests are daily-close only: no intrabar fills, no simulated limit orders, no intraday strategies at all — the engine rebalances in one scheduled trading period per day.
• Symphonies are long-only stocks and ETFs. Options are traded by hand from the chain rather than automated by a strategy, and short selling and margin are not on offer. No futures, no forex, no crypto.
• The MCP server is unmaintained and half-abandoned. Its GitHub repository now 404s, the last release was 0.1.7 in July 2025, and the hosted variant the vendor's Claude Desktop extension still points at (mcp.composer.trade) no longer resolves. The PyPI package and the REST API behind it do still work, so installing it by name is the only route that does.
• Nothing is portable. There is no self-hosted build, and the strategy language is Composer's — a symphony does not leave for another broker.

Alternatives

QuantConnect and the Python backtesting libraries if you would rather write code and keep the result portable. TrendSpider for no-code automation attached to charts rather than a brokerage. AmiBroker or Wealth-Lab if a desktop licence and your own data suit you better than a subscription that also holds the money.