Hammer

Install and import#

npm install fintech-algorithms

import { hammer } from "fintech-algorithms/price-action-and-candlesticks/single-candle-patterns/hammer";

Signature#

hammer(inputs)

Evaluates one candle against explicit hammer geometry, scale, and downtrend context conventions.

Parameters#

Returns#

{ topic_id, pattern, matched, state, direction, trend_context, required_context, body, upper_shadow, lower_shadow, range, body_scale, range_scale, history_count, geometry_score, checks, failed_checks }

One pattern record. state is warmup, wrong-context, matched, or not-matched; this is not a positional series.

Warm-up#

The first 5 prior observations positions are state: warmup. The detector returns one readiness record before five prior body/range observations are available; it does not emit a positional null prefix.

Errors#

• When OHLC, history, context, or tick-size input violates the data contract — throws

Complexity: time , space .

Worked example#

executed Captured by running this function on the input its own test provides. Real output of real code — but not asserted against a published figure.

Input#

{
  "current": {
    "open": 102,
    "high": 103.2,
    "low": 100,
    "close": 103
  },
  "prior_bodies": [2, 2.2, 1.8, 2.1, 1.9, 2],
  "prior_ranges": [5, 5, 5, 5, 5, 5],
  "trend_context": "downtrend",
  "tick_size": 0.1
}

Call#

hammer(inputs)

Returns#

object with 17 fields: topic_id, pattern, matched, state, direction, trend_context, required_context, body, …

{
  "topic_id": "D06-F02-A06",
  "pattern": "Hammer",
  "matched": true,
  "state": "matched",
  "direction": "bullish",
  "trend_context": "downtrend",
  "required_context": "downtrend",
  "body": 1,
  "upper_shadow": 0.20000000000000284,
  "lower_shadow": 2,
  "range": 3.200000000000003,
  "body_scale": 2,
  "range_scale": 5,
  "history_count": 10
}

Showing 14 of 17 fields.

Other exports#

This module also exports calculate, shadowToBodyRatio, gapClassification, trendContextFilter, doji, dragonflyDoji, gravestoneDoji, marubozu, spinningTop, hangingMan, invertedHammer, shootingStar, bullishEngulfing, bearishEngulfing, bullishHarami, bearishHarami, piercingLine, darkCloudCover, tweezerTop, tweezerBottom. Every module additionally exports run as an alias of its primary function, and a meta object carrying its catalog id, domain, family, shape and article URL.

Diagrams#

Calculation flow#

flowchart LR
    S1["Validate the candle tick context and aligned prior sca"]
    S2["Calculate body upper shadow lower shadow and prior med"]
    S3["Evaluate the Hammer Boolean checks in formula order"]
    S4["Apply required context when applicable and return ever"]
    S1 --> S2
    S2 --> S3
    S3 --> S4
    S4 --> D{"the material geometry threshold at exact equality"}
    D --> O["matched + diagnostics"]
    O --> A["Audit: A matched output has no failed Boolean checks"]

How it works#

This page states the contract — how to call it correctly. The article explains the concept: why it works, and where it breaks.

Read the article →

References#

• Japanese Candlestick Charting Techniques, Second Edition — Steve Nison
• CMT Program Guide 2026 — CMT Association
• Candlestick Settings — TA-Lib project
• Hammer recognizer — TA-Lib project
• Evidence boundary

The rest of the Single-Candle Patterns family#

• DojiEvaluates one candle against the repository's explicit doji geometry and scale convention.
• Dragonfly DojiEvaluates one candle against the repository's explicit dragonfly-doji geometry and scale convention.
• Gravestone DojiEvaluates one candle against the repository's explicit gravestone-doji geometry and scale convention.
• MarubozuEvaluates one candle against the repository's explicit marubozu geometry and scale convention.
• Spinning TopEvaluates one candle against the repository's explicit spinning-top geometry and scale convention.
• Hanging ManEvaluates one candle against explicit hanging-man geometry, scale, and uptrend context conventions.
• Inverted HammerEvaluates one candle against explicit inverted-hammer geometry, scale, and downtrend context conventions.
• Shooting StarEvaluates one candle against explicit shooting-star geometry, scale, and uptrend context conventions.
• Long-Legged DojiMarks each bar whose body is a small fraction of its high-low span while both shadows are long, and reports how much slack the …
• Four-Price DojiMarks each bar whose entire range and whose open-to-close distance both sit within a tick tolerance, the degenerate candle wher…
• High-Wave CandleMarks each bar with a small body relative to its high-low span whose two shadows are both a multiple of that body, the long-tai…
• Belt HoldMarks each bar that opens at one extreme of its own range within a tick and closes at least 60 percent of the span away, and re…