painstaking

/ˈpeɪnzteɪkɪŋ/
adjective
  1. Done with very careful, thorough, and diligent effort; showing great attention to detail.
    • The artist did painstaking work on the tiny details of the portrait.
    • The restoration of the ancient manuscript required painstaking effort.
    • Her painstaking research uncovered facts that others had missed.