How do I punish a slow move in the opening?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws and is regression-tested against the official 110-diagram repetition casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it against the engine before publishing.
Direct answer
Use the extra tempo to develop faster and aim it at whatever the slow move left undefended. A move that develops nothing, like an early advisor shuffle, is a free move for you, but only if you actually spend it on something useful rather than matching the opponent's pace.
Identify what got weaker
Every slow move has a cost even if it defends nothing new: a palace point vacated, a file left uncontested, a horse's leg unblocked. Find that specific cost and aim your development at it rather than attacking in general.
Do not rush the strike
A tempo advantage is worth converting into a second attacking piece before committing to a threat, not worth cashing in immediately with a single piece. One attacker still achieves nothing, however far ahead on development you are.
Related questions
What counts as a slow move?
Anything that neither develops a new piece nor answers a real threat, most often an early advisor or elephant shuffle.
Should I always punish it immediately?
No. Bank the tempo, keep developing, and strike once you have the second attacker the plan needs.
.