A trendline is diagonal support or resistance: connect rising swing lows in an uptrend (support line below price) or falling swing highs in a downtrend (resistance line above). Where horizontal support/resistance marks prices the market remembers, a trendline marks the rhythm of a trend — and when that rhythm holds, it hands you both an entry location and a clean invalidation.

Trendlines have a deserved reputation problem: drawn badly, they're astrology. Drawn honestly, they're a solid framework. The difference is entirely in the rules below.

Drawing rules (non-negotiable)

1. Two swings define, the third confirms. Any two points make a line; only a third touch that respects it proves the market sees it too. Trade touches three and four — not two.
2. Connect wicks or bodies — consistently. Pick a convention and keep it; switching per-line to make things fit is curve-fitting.
3. Never redraw to rescue a broken line. If price closes through it, it's broken. Adjusting the line to keep the story alive is the classic trendline sin.
4. Steepness is fragility. Lines over ~45° get broken by mere sideways drift; sustainable trends draw shallower lines. A trend that keeps steepening needs a new, steeper line — and that steepest line breaking is often the first reversal warning.

Strategy 1: The third-touch bounce

• Timeframe: 1H–daily
• Setup: established uptrend line with two clear touches; price descending toward touch three, higher-timeframe trend still up
• Entry trigger: rejection candle at the line — hammer or bullish engulfing
• Stop-loss: below the line and below the trigger candle's low
• Target: the prior swing high, then trail; the line itself trails your stop on later touches
• Short: mirror on downtrend lines

Strategy 2: The break and retest

Trendline breaks end rhythms, and the retest is the entry:

• Setup: a mature trendline (3+ touches) breaks with a full candle close through it
• Entry: on the retest from the other side — price returns to the broken line and rejects it (role reversal, same as horizontal levels)
• Stop: beyond the retest swing
• Target: the most recent major swing in the new direction

A trendline break is not an automatic reversal — most lead to sideways consolidation first. The retest requirement filters the difference between a rhythm ending and a trend reversing.

How to backtest it

Drawing discipline is the whole game, so test it with the future hidden:

1. In chart replay, pause and draw your lines at a random historical moment; write down which touch counts you'd trade.
2. Play forward candle by candle. No redrawing broken lines — log the break instead.
3. 50 trades per the backtesting method, tagged bounce or break-retest.
4. Grade your lines like levels: which held to touch four? Which were fantasy? Your drawing improves faster than any tutorial can teach because the market grades you instantly.

Common mistakes

1. Trading touch two — the line isn't real yet.
2. Redrawing to avoid admitting the break — the market broke your line, not your feelings.
3. Steep-line faith — parabolic lines break on any pause; expect it.
4. Trendlines alone — confluence with a horizontal level or the 50 EMA doubles the quality of any touch.

FAQ

Are trendlines reliable?

Honestly drawn (3+ touches, never redrawn, reasonable slope) and traded with a trigger candle, they perform comparably to horizontal levels. The unreliability people complain about is usually their drawing, not the tool — replay 50 of them and grade yourself.

Wicks or bodies when drawing trendlines?

Both are defensible; wicks are the common convention. What matters is consistency — and treating the line as a zone with the same wick-tolerance you'd give horizontal support.

What timeframe is best for trendline trading?

4H and daily lines are respected most and whipsaw least. Intraday lines work but break constantly — fine for scalping context, poor as standalone signals.