In this paper we show that a Brownian Gibbsian line ensemble whose top curve approximates a parabola must be given by the parabolic Airy line ensemble. More specifically, we prove that if $\boldsymbol{\mathcal{L}} = (\mathcal{L}_{1}, \mathcal{L}_{2}, \ldots )$ is a line ensemble satisfying the Brownian Gibbs property, such that for any $\varepsilon > 0$ there exists a constant $\mathfrak{K} (\varepsilon ) > 0$ with then $\boldsymbol{\mathcal{L}}$ is the parabolic Airy line ensemble, up to an independent affine shift. Specializing this result to the case when $\boldsymbol{\mathcal{L}} (t) + 2^{-1/2} t^{2}$ is translation-invariant confirms a prediction of Okounkov and Sheffield from 2006 and Corwin–Hammond from 2014.