Quality education can be achieved with the support of competent teachers. To continuously improve teacher competency, training, development, and mentoring are conducted. This research aims to develop GSites as an e-learning medium that facilitates flexible mentoring activities, thus providing teachers with the opportunity to independently deepen their training material. The development of GSites uses an adapted Borg & Gall approach. Data collection in this research includes questionnaires, interviews, and observations, followed by quantitative and qualitative analysis. The trials were conducted three times: the initial trial with website experts, a limited trial with 5 teachers, and a field trial with 28 teachers. The research results show product validation by website and external experts at 89.29%, indicating that the product is valid and suitable for use. The limited teacher trial and field implementation trial was conducted once. The limited trial results show scores of 3.67 and 91.67% for ease and practicality, e-learning structure 3.52 and 88.00%, and communication 3.57 and 89.17%. The field trial results show scores of 3.39 and 84.67% for ease and practicality, e-learning structure at 3.53 and 88.15%, and communication at 3.55 and 88.84%. The results indicate that GSites is attractive, very simple and practical, structured, and highly communicative. / Pendidikan yang berkualitas dapat diwujudkan apabila didukung guru yang kompeten, agar kompetensi guru terus meningkat, maka dilakukan pelatihan, pengembangan, dan mentoring. Tujuan penelitian ini untuk mengembangkan GSites sebagai media e-learning kegiatan mentoring dengan memberikan kesempatan belajar mandiri dalam menyusun modul ajar literasi numerasi. Pengembangan GSites menggunakan pendekatan Borg & Gall yang disesuaikan. Pengumpulan data pada penelitian ini berupa angket, wawancara dan observasi, selanjutnya dilakukan analisis kuantitatif dan kualitatif. Uji coba dilakukan sebanyak 3 kali, uji coba awal kepada ahli website, uji terbatas kepada 5 orang guru, dan uji lapangan terhadap 28 guru. Hasil validasi yang dilakukan ahli website dan ahli eksternal sebesar 89,29%, menunjukkan produk yang dibuat valid dan layak digunakan. Uji coba terbatas guru dan uji coba pelaksanaan lapangan dilakukan sebanyak satu kali. Hasil uji coba terbatas menunjukkan hasil 3,67 dan 91,67% untuk kemudahan dan kepraktisan, struktur e-learning 3,52 dan 88,00%, dan komunikasi 3,57 dan 89,17%. Hasil uji coba lapangan menunjukkan 3,39 dan 84,67 %, untuk kemudahan dan kepraktisan, struktur e-learning 3,53 dan 88,15%, dan komunikasi 3,55 dan 88,84%. Produk yang dihasilkan menunjukkan bahwa GSites menarik, sangat sederhana dan praktis, terstruktur, dan sangat komunikatif.