Build and verify a script · Flowscope Script

A short path from an idea to a checked indicator: data coverage, warm-up, stable signals, runtime checks and common mistakes.

Start with the smallest working signal. Add a dashboard, extra markets and alerts after the signal has been checked. This is also the recommended workflow for the AI assistant.

Decide what the signal promises

State the market and chart interval, the condition for long and short, and when the condition becomes knowable. Use these defaults unless the trader asks for something else:

Decisions on on chart.close, using confirmed higher-timeframe values.
Live previews in on chart.update, clearly named as developing.
Entries marked at detection time, never moved to an earlier pivot.
No invented substitute for missing market data. A missing filter blocks a signal; it does not become a neutral or passing filter via ?? 0.0.

A pivot with three right bars requires three later bars. It cannot be both confirmed and known on the pivot bar. A structural line may point back to that pivot, but an entry marker must show when the pivot was detected. For an earlier signal, change the rule to a causal condition such as a break of an already known level; explain that this is a different signal. See repainting.

Check the data before writing the full script

The chart host builds period subscriptions from loaded chart bars. Requested timeframes must be whole multiples of the chart interval: a 5s chart can supply 1m bars, but a 1m chart cannot supply 5s bars. Declaring a subscription does not fetch an independent, unlimited history for it.

Count source bars, not chart bars. Fifty hourly candles require at least 50 hours of history (36,000 bars on a 5s chart), plus room for alignment and warm-up. A seeded EMA may return a number with much less history; a number alone does not prove that its warm-up is adequate. Loading more history can change its seed and early values.

Other-market subscriptions on charts currently support ohlcv, vd and cvd. The quant lab does not supply other-market subscriptions, order-book snapshots or volume profiles. It rejects those requests rather than treating unavailable data as a successful study with no trades. Run those strategies on the chart and inspect the Strategy Tester instead.

Use the shortest verification loop

Read chart_context. Select one relevant example and use lookup_builtins for uncertain signatures; names and arguments are case-sensitive.
Write a minimal, formatted script with named inputs and bounded collections. Read only the subscriptions the calculation needs.
Call check_script. It compiles, evaluates setup and checks timeframe/data requirements against the active chart without running handlers. Fix errors; inspect the reported number of confirmed bars and warm-up needs.
Call apply_script once the checks pass. Inspect runtime errors, computation time, actual subscription coverage, plotted values and marks. Empty output is a finding to investigate, not proof that no trading opportunities exist.
Use look_at_chart to check placement and readability. For a strategy, inspect run_backtest, its tested period, costs and trade count.
For a stability claim, step replay across a signal and across a higher-timeframe boundary. Record the detection bar. Advance several bars and compare it with the same period after replay/reload using the same inputs and source history.

Compilation, successful execution, visible output and signal stability are four separate checks. Report which actually passed. A screenshot alone cannot verify that historical signals never changed.

Common mistakes and direct fixes

Symptom	Check or fix
Compiles, but nothing appears	Subscription coverage, compatible timeframes, nulls, warm-up and signal conditions
EMA or cross behaves differently after a filter change	Evaluate every `ta.*` call on every event of its intended clock, then filter its result; do not hide stateful calls inside `if` or short-circuit expressions
Higher-timeframe EMA changes too often	Calculate it in `on higher.close` and store its result in `state`; do not feed repeated higher closes to a chart-clock EMA
Entry suddenly appears several bars back	Pivot confirmation delay, negative `offset`, or an explicit past timestamp; separate pivot location from detection time
Live arrow appears and vanishes	Forming data or an update handler; offer a separate confirmed signal
Indicator trails the price	Distinguish candle-close waiting, pivot confirmation, indicator smoothing and computation time before changing the rule
Slow chart or budget error	Remove per-bar scans, prefer `ta.*` or bounded rolling aggregates, draw status cards only under `isLast`

For runtime limits and browser scheduling, see performance.