Engine API

Three ways to run a script: the quas command line, the quas serve worker protocol, and the terminal's HTTP endpoints (which use quas serve behind the scenes). All three return the same result format, described at the end of this chapter.

Command line

Exit status: 0 success, 2 compile or run error (the message is on stderr; compile errors list line:col code: message and the fix when there is one).

The `quas serve` worker

quas serve reads one JSON request per line on stdin and writes one JSON response per line on stdout, in order. Compiled programs are cached by content (the script and its libraries), and sessions keep the engine state of one script on one chart alive, so new bars and price updates execute only the bars that changed.

Every response has id (echoed from the request), ok, op, ms (time in the worker) and timing: {parseMs, execMs, encodeMs}. A failure is {"ok": false, "error": {"code": "COMPILE" | "LIMIT_EXCEEDED" | "REQUEST", "message": ..., "diagnostics": [...]}}.

open

{"op": "open", "id": 1, "session": "chart-1:ema",
 "script": "analysis \"EMA\" { overlay = true }\nrender.line(ta.ema(close, 20), \"EMA\")\n",
 "libraries": [{"name": "viz/palette", "source": "library \"viz/palette\" ..."}],
 "bars": {"time": [1700000000, 1700000060], "open": [100, 101], "high": [102, 103],
          "low": [99, 100], "close": [101, 102], "volume": [500, 450]},
 "params": {"length": 20}, "asset": {"ticker": "BTCUSDT", "timezone": "UTC", "tick_size": 0.1},
 "formingLast": true, "encoding": "json", "view": {"from": 0, "to": 1}}

bars.book carries the real order book of each bar, one snapshot (or null) per bar:

"book": [
  {"bids": [[100.9, 12, 3], [100.8, 30]], "asks": [[101.1, 8, 1], [101.2, 25]]},
  {"bids": [[101.0, 5]], "asks": [[101.2, 9]]},
  {"orders": [["bid", 101.0, 2, 9001], ["ask", 101.3, 4, 9002]]},
  null
]

A level is [price, size, orders?] (or {"price", "size", "orders"}), best price first: one level a side is L1, more are L2. orders (L3) lists individual orders as [side, price, size, id?] (side -1 / 1 or "bid" / "ask" / "buy" / "sell"); when a snapshot has orders and no levels, the levels are aggregated from the orders. append takes the same field; update_last takes one snapshot as "book" on its bar and replaces the forming bar's book. schema.hostData lists the host data the script reads (order_book, order_flow, derivatives, fundamentals) and schema.bookDepth the depth it needs (1 L1, 2 L2, 3 L3), so a host sends the book only to scripts that use it.

The response has session, key (program hash), schema (the outputs, see below), bars, from (0), forming and the outputs of every bar.

append, update_last, view, close

{"op": "append", "session": "chart-1:ema", "formingLast": true,
 "bars": {"time": [1700000120], "open": [102], "high": [102], "low": [102], "close": [102], "volume": [0]}}
{"op": "update_last", "session": "chart-1:ema",
 "bar": {"time": 1700000120, "open": 102, "high": 103.5, "low": 101.8, "close": 103.1, "volume": 220}}
{"op": "view", "session": "chart-1:ema", "from": 400, "to": 900}
{"op": "close", "session": "chart-1:ema"}

• append adds newer bars. A first bar whose time equals the last bar's time replaces it (that is how a forming bar is confirmed with its final prices).
• update_last replaces the prices of the forming bar and re-executes only that bar.
• The response of append / update_last contains the outputs of bars from .. bars - 1 only: replace your copy from index from on. Strategy trades come from tradesFrom on, the equity curve from equityFrom on, bot signals only for the new bars.
• view recomputes visible-range profiles only.
• Other ops: run (open + close in one, no session), check (compile only: valid, schema, symbols, diagnostics), stats (sessions, cached programs, cache hits), ping.

HTTP endpoints (terminal)

All endpoints take and return JSON. session and check require a signed-in user (bearer token or the session cookie) and answer 401 otherwise; session ids are private to the user.

POST /api/quascript/session

The worker protocol above, one operation per request. The body is the request object (op, session, ...); libraries named by use are added from the bundled library folder when the client does not send them. The response is the worker's response, unchanged.

POST /api/quascript/check

{ "script": "...", "libraries": [...] } → { ok, valid, key, schema, symbols, diagnostics }. Each diagnostic has code, severity, message, note, line, col, endLine, endCol and fixes: [{line, col, endLine, endCol, text}]. Used by the editor for underlines and quick fixes.

POST /api/quascript/run

One complete run in the chart's format: { script, bars: [{time, open, high, low, close, volume}], params, libraries, asset } → { success, data } where data has plots (with data: [{time, value, color?}]), markers + markSites, hlines, fills, candleColors, backgrounds, drawings, alerts, strategy and meta.timing. Settings are matched to the script's parameters by id or title. Use session for live charts; run recomputes everything.

Configuration

Result format (schema version 2)

A full result (quas run) is one JSON object:

Plot metadata: index title style color width stroke pane offset base upColor downColor shape size dynamicColor backend priceIndex profileIndex box. Styles: 0 line, 1 histogram, 2 area, 4 dots, 5 spline, 6 step, 7 baseline, 8 .. 17 price styles, 13 volume profile, 18 stepped area, 20 session profile, 21 TPO, 26 level. Strokes: 0 solid, 1 dashed, 2 dotted.

Colors are numbers 0xAARRGGBB: the low 24 bits are RGB and the high byte is the opacity, with 0 meaning fully opaque (so plain palette colors are just 0xRRGGBB). In per-bar color arrays null means "the plot's color" and 0 is black.