Abstract A measurement for inclusive 2- and 3-jet events of the azimuthal correlation between the two jets with the largest transverse momenta, $$\varDelta \phi _{12}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Δ</mml:mi><mml:msub><mml:mi>ϕ</mml:mi><mml:mn>12</mml:mn></mml:msub></mml:mrow></mml:math> , is presented. The measurement considers events where the two leading jets are nearly collinear (“back-to-back”) in the transverse plane and is performed for several ranges of the leading jet transverse momentum. Proton-proton collision data collected with the CMS experiment at a center-of-mass energy of $$13\,\text {Te}\text {V} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>13</mml:mn><mml:mspace /><mml:mrow><mml:mtext>Te</mml:mtext><mml:mspace /></mml:mrow></mml:mrow></mml:math> and corresponding to an integrated luminosity of $$35.9{\,\text {fb}^{-1}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>35.9</mml:mn><mml:mrow><mml:mspace /><mml:msup><mml:mtext>fb</mml:mtext><mml:mrow><mml:mo>-</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:mrow></mml:math> are used. Predictions based on calculations using matrix elements at leading-order and next-to-leading-order accuracy in perturbative quantum chromodynamics supplemented with leading-log parton showers and hadronization are generally in agreement with the measurements. Discrepancies between the measurement and theoretical predictions are as large as 15%, mainly in the region $$177^\circ&lt; \varDelta \phi _{12} &lt; 180^\circ $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mn>177</mml:mn><mml:mo>∘</mml:mo></mml:msup><mml:mo>&lt;</mml:mo><mml:mi>Δ</mml:mi><mml:msub><mml:mi>ϕ</mml:mi><mml:mn>12</mml:mn></mml:msub><mml:mo>&lt;</mml:mo><mml:msup><mml:mn>180</mml:mn><mml:mo>∘</mml:mo></mml:msup></mml:mrow></mml:math> . The 2- and 3-jet measurements are not simultaneously described by any of models.