The structure of embedded relative clauses in English may involve several grammatical elements, generating different grammatical rules with respect to word order. Studying the impact of first language (L1) transfer in the production of English embedded relative clauses is important to reveal valuable information about specific challenges in second language acquisition (SLA). Online methods used by researchers to measure the degree to which the L1 impacts the processing and learning of a second language (L2) have limitations regarding measurement of L1 transfer in English embedded relative clauses. Therefore, the purpose of this thesis is to present a new tool that enables the assessment of how structures in Swedish affect learning English as an L2, with special respect to embedded relative clauses. A new online tool, LinguaMapping, was developed by the author of this thesis, which enables the detection of Swedish L1 transfer in Englishembedded relative clauses. LinguaMapping is also proved to be more accessible, affordable, and sustainable than the online methods eye-tracking and self-paced reading. In the future, the supervisor of this project will submit LinguaMapping for pilot testing prior to conducting main studies of embedded relative clauses as well as other L2 phenomena to shed light on the role of L1 transfer in shaping L2 proficiency.