The term serverless is often used to describe cloud applications that comprise components managed by third parties. Like any other cloud application, serverless applications are often tightly-coupled with providers, their features, models, and APIs. As a result, when their portability to another provider has to be assessed, application owners must deal with identification of heterogeneous lock-in issues and provider-specific technical details. Unfortunately, this process is tedious, error-prone, and requires significant technical expertise in the domains of serverless and cloud computing. In this work, we introduce SEAPORT, a method for automatically assessing the portability of serverless applications with respect to a chosen target provider or platform. The method introduces (i) a canonical serverless application model, and (ii) the concepts for portability assessment involving classification and components similarity calculation together with the static code analysis. The method aims to be compatible with existing migration concepts to allow using it as a complementary part for serverless use cases. We present an architecture of a decision support system supporting automated assessment of the given application model with respect to the target provider. To validate the technical feasibility of the method, we implement the system prototypically.