Can I use apps or devices to read greens?

No, you cannot use an app or device that measures slope, recommends a line of play, or acts as a level. Rule 4.3a prohibits equipment that artificially eliminates the skill of reading a green, though you may still use your club as a plumb line.

What the rule says about green reading

Rule 4.3a forbids using equipment that artificially reduces the need for the judgment and skill essential to golf. For putting greens, this means you may not use a device to measure elevation changes, interpret directional information to get a recommended line, or use any alignment device. The rule targets anything that does the reading for you — whether it's a phone app, a digital map, or a physical level.

What you can and cannot do on the green

You are allowed to consult a paper or electronic green map, but only if its size and scale stay within the limits set by Clarification 4.3a/1 — essentially, a basic diagram that still requires you to judge the break yourself. You may not use a bubble level (including a phone's built-in level), a bottled drink as a level, a weight on a string, or any app that processes slope data and tells you where to aim. Using your club as a plumb line to feel the slope is explicitly permitted.

Penalties and committee options

A breach of Rule 4.3a carries the general penalty: two strokes in stroke play, loss of hole in match play. A committee may go further by adopting Model Local Rule G-12, which prohibits all green-reading materials entirely. If that Local Rule is in effect, even a simple paper diagram is not allowed.

Exceptions that change the answer

• You use your club as a plumb line to gauge slope → That is allowed under Clarification 4.3a(1)/1; the club is not treated as an artificial level.
• The committee adopts Model Local Rule G-12 → All green-reading materials — paper or digital — are prohibited for strokes from the putting green.

Frequently asked questions

Can I use a green-reading app that shows arrows or a recommended line?

No. Any app that interprets slope data and gives you a recommended line of play breaches Rule 4.3a because it eliminates the essential skill of reading the green yourself.

Is it okay to use my phone's bubble level on the green?

No. Clarification 4.3a(1)/1 explicitly forbids using a bubble level — including a phone app that functions as one — to gauge slope.

Can I look at a detailed green map on my phone between putts?

Only if the map's size and scale comply with Clarification 4.3a/1. Overly detailed digital maps that effectively read the break for you are not permitted.

What if my playing partner uses a prohibited green-reading app?

They incur the general penalty (two strokes or loss of hole). You are not penalized for their breach, but you should remind them of the rule.

Does Rule 4.3 ban all electronic devices on the course?

No. You may use a distance-measuring device for yardage, check weather forecasts, or record stats for post-round analysis. The restriction applies only to equipment that interprets slope or recommends a line during the round.