diff --git a/Makefile b/Makefile
index 9c98d6d..7a2e0f2 100644
--- a/Makefile
+++ b/Makefile
@@ -47,9 +47,10 @@ MODULES = $(filter-out $(OBJDIR)/main%,$(OBJECTS))
 # Build outputs
 GRAY      = $(BINDIR)/gray
 LIBGRAY   = $(LIBDIR)/libgray.so
-BINARIES  = $(GRAY)
+BINARIES  = $(GRAY) $(GRAY)-convert
 LIBRARIES = $(LIBGRAY)
-MANPAGES  = $(addprefix $(SHAREDIR)/,gray.1 gray.ini.5 profiles.txt.5 beamdata.txt.5 magneticdata.txt.5)
+MANPAGES  = $(addprefix $(SHAREDIR)/,gray.1 gray-convert.1 gray.ini.5 \
+						  profiles.txt.5 beamdata.txt.5 magneticdata.txt.5)
 
 ##
 ## Git information (used in the version string)
@@ -149,6 +150,10 @@ $(OBJDIR)/%.o: $(OBJDIR)/%.d
 $(GRAY): $(OBJDIR)/main.o $(LIBGRAY) | $(BINDIR)
 	$(LD) $(LDFLAGS) -o '$@' $< -lgray
 
+# gray-convert binary
+$(GRAY)-convert: $(OBJDIR)/main_convert.o $(LIBGRAY) | $(BINDIR)
+	$(LD) $(LDFLAGS) -o '$@' $< -lgray
+
 # GRAY shared library
 $(LIBDIR)/libgray.so: $(MODULES) | $(LIBDIR)
 	$(LD) -shared $(LDFLAGS) -o '$@' $^
@@ -173,6 +178,8 @@ $(SHAREDIR)/doc: | $(SHAREDIR)
 # Generated man pages
 $(SHAREDIR)/gray.1: $(GRAY) doc/man/gray.1 | $(SHAREDIR)
 	help2man '$<' -i doc/man/gray.1 -N -n 'beam-tracing code for EC waves' > '$@'
+$(SHAREDIR)/gray-convert.1: $(GRAY)-convert | $(SHAREDIR)
+	help2man '$<' -N -n 'configuration format converter' > '$@'
 
 $(SHAREDIR)/%: doc/man/%.md $(GRAY) | $(SHAREDIR)
 	pandoc -s '$<' -t man \
diff --git a/doc/man/gray.1 b/doc/man/gray.1
index 7f43cf2..7855164 100644
--- a/doc/man/gray.1
+++ b/doc/man/gray.1
@@ -13,7 +13,8 @@ GRAY main configuration file
 Legacy configuration file
 
 This file allows configuring all the parameters of a GRAY simulation, including
-all other input files.
+all other input files. Existing files can be upgraded to the gray.ini format
+using the \fBgray-convert\fR(1) tool.
 .TP
 .I beamdata.txt
 Beam description file
@@ -41,4 +42,5 @@ location can be changed with the \fB-o\fR option.
 For a list of the unit numbers and their descriptions see the GRAY user manual.
 
 [SEE ALSO]
-\fBgray.ini\fR(5), \fBgray_params.data\fR(5), \fBbeamdata.txt\fR(5), \fBprofiles.txt\fR(5)
+\fBgray-convert\fR(1), \fBgray.ini\fR(5), \fBgray_params.data\fR(5),
+\fBbeamdata.txt\fR(5), \fBprofiles.txt\fR(5)
diff --git a/src/gray_cli.f90 b/src/gray_cli.f90
index ce4b431..7288cfb 100644
--- a/src/gray_cli.f90
+++ b/src/gray_cli.f90
@@ -24,7 +24,8 @@ module gray_cli
 
   private
   public :: cli_options, print_cli_options, parse_cli_options, &
-            deinit_cli_options, parse_param_overrides
+            deinit_cli_options, parse_param_overrides, &
+            print_version, get_next_command
 
 contains
 
diff --git a/src/main_convert.f90 b/src/main_convert.f90
new file mode 100644
index 0000000..aa6f95a
--- /dev/null
+++ b/src/main_convert.f90
@@ -0,0 +1,340 @@
+program gray_convert
+
+  use gray_cli,    only: print_version, get_next_command
+  use gray_params, only: gray_parameters, read_gray_params, read_gray_config, &
+                         step_enum, absorption_enum, current_drive_enum,      &
+                         polar_enum, beam_enum, equil_enum, x_point_enum,     &
+                         scaling_enum, rho_enum, profiles_enum
+  implicit none
+
+  ! Configuration formats
+  enum, bind(c)
+    enumerator :: config_format = -1
+    enumerator :: FORMAT_PARAMS = 1 ! the legacy gray_params.data format
+    enumerator :: FORMAT_INI    = 2 ! the current INI format
+  end enum
+
+  ! Command line options
+  ! See print_help() for a description.
+  type cli_options
+    character(len=:), allocatable :: input_file   ! file to read
+    character(len=:), allocatable :: output_file  ! file to write
+    integer(kind(config_format))  :: format       ! output file format
+  end type
+
+  type(cli_options) :: opts
+  type(gray_parameters) :: params
+  integer :: err
+
+  call parse_cli_options(opts)
+
+  ! Reading
+  if (index(opts%input_file, ".data") /= 0) &
+    call read_gray_params(opts%input_file, params, err)
+  if (index(opts%input_file, ".ini") /= 0) &
+    call read_gray_config(opts%input_file, params, err)
+
+  if (err /= 0) call exit(2)
+
+  ! Writing
+  select case (opts%format)
+    case (FORMAT_PARAMS)
+      print '(a)', 'gray_params.data output not implemented!'
+      call exit(1)
+    case (FORMAT_INI)
+      call write_gray_config(opts%output_file, params)
+  end select
+
+  call exit(0)
+
+contains
+
+  subroutine print_help()
+    ! Prints the usage screen
+
+    print '(a)', 'Usage: gray-convert [options] INFILE OUTFILE'
+    print '(a)', ''
+    print '(a)', 'Converts between different GRAY configuration formats.'
+    print '(a)', ''
+    print '(a)', 'Options:'
+    print '(a)', '  -h, --help                display this help and exit'
+    print '(a)', '  -V, --version             display version information and exit'
+    print '(a)', '  -f, --format              set the output file format (default: ini)'
+    print '(a)', '                            valid formats are: `ini`, `params`.'
+    print '(a)', ''
+    print '(a)', '*Exit status*'
+    print '(a)', ' 0  if OK,'
+    print '(a)', ' 1  if technical problems   (e.g., invalid arguments, missing input files),'
+    print '(a)', ' 2  if serious trouble      (e.g., invalid input file).'
+  end subroutine
+
+  subroutine parse_cli_options(opts)
+    ! Parses the CLI arguments and initialise the options
+
+    ! subroutine arguments
+    type(cli_options), intent(out) :: opts
+
+    ! local variables
+    character(len=:), allocatable :: argument
+    integer :: i, nargs
+
+    ! Default option values
+    opts%format = FORMAT_INI
+
+    nargs = command_argument_count()
+    i = 1
+
+    do
+      if (i > nargs) exit
+      call get_next_command(i, argument)
+
+      ! parse an argument (and possibly a value)
+      select case (argument)
+        ! parse optional arguments
+        case ('-h', '--help')
+          call print_help()
+          deallocate(argument)
+          call exit(0)
+
+        case ('-V', '--version')
+          call print_version()
+          deallocate(argument)
+          call exit(0)
+
+        case ('-f', '--format')
+          call get_next_command(i, argument)
+          select case (argument)
+            case ('params')
+              opts%format = FORMAT_PARAMS
+            case ('ini')
+              opts%format = FORMAT_INI
+            case default
+              print '(a)', 'unknown format: ', argument
+          end select
+
+        case default
+          ! read positional arguments
+          if (i - nargs == 0) then
+            opts%input_file = argument
+            cycle
+          else if (i - nargs == 1) then
+            opts%output_file = argument
+            cycle
+          end if
+
+          print '(a,a,/)', 'Unknown option: ', argument
+          call print_help()
+          deallocate(argument)
+          call exit(1)
+
+      end select
+    end do
+
+    ! free temporary string
+    if (nargs > 0) deallocate(argument)
+  end subroutine
+
+  subroutine write_gray_config(filename, params)
+    ! Generates a gray.ini configuration file
+
+    ! subroutine arguments
+    character(len=*),       intent(in) :: filename
+    type(gray_parameters),  intent(in) :: params
+
+    ! local variables
+    type(gray_parameters) :: defaults
+    character(*), parameter :: fmt = '(a, " = ", g0.6)'
+    integer :: err, u
+
+    open(u, file=filename, action='write', iostat=err)
+    if (err /= 0) then
+      print '("opening output file (",a,") failed!")', filename
+      return
+    end if
+
+    write(u, '(a)') "[raytracing]"
+    write(u, fmt) "nrayr",  params%raytracing%nrayr
+    write(u, fmt) "nrayth", params%raytracing%nrayth
+    if (params%raytracing%rwmax /= defaults%raytracing%rwmax) &
+      write(u, fmt) "rwmax", params%raytracing%rwmax
+    if (params%raytracing%igrad /= defaults%raytracing%igrad) &
+      write(u, fmt) "igrad", params%raytracing%igrad
+    if (params%raytracing%ipass /= defaults%raytracing%ipass) &
+      write(u, fmt) "ipass", params%raytracing%ipass
+    if (params%raytracing%ipol .neqv. defaults%raytracing%ipol) &
+      write(u, fmt) "ipol", format_bool(params%raytracing%ipol)
+    write(u, fmt) "dst",   params%raytracing%dst
+    if (params%raytracing%nstep /= defaults%raytracing%nstep) &
+      write(u, fmt) "nstep", params%raytracing%nstep
+    if (params%raytracing%idst /= defaults%raytracing%idst) &
+      write(u, fmt) "idst",  format_step(params%raytracing%idst)
+
+    write(u, '(/,a)') "[ecrh_cd]"
+    if (params%ecrh_cd%iwarm /= defaults%ecrh_cd%iwarm) &
+      write(u, fmt) "iwarm", format_absorp(params%ecrh_cd%iwarm)
+    if (params%ecrh_cd%ieccd /= defaults%ecrh_cd%ieccd) &
+      write(u, fmt) "ieccd", format_current(params%ecrh_cd%ieccd)
+    if (params%ecrh_cd%ilarm /= defaults%ecrh_cd%ilarm) &
+      write(u, fmt) "ilarm", params%ecrh_cd%ilarm
+    if (params%ecrh_cd%imx /= defaults%ecrh_cd%imx) &
+      write(u, fmt) "imx", params%ecrh_cd%imx
+
+    write(u, '(/,a)') "[antenna]"
+    write(u, fmt) "alpha", params%antenna%alpha
+    write(u, fmt) "beta",  params%antenna%beta
+    if (params%antenna%power /= defaults%antenna%power) &
+      write(u, fmt) "power", params%antenna%power
+    write(u, fmt) "iox",  format_polar(params%antenna%iox)
+    write(u, fmt) "ibeam",  format_beam(params%antenna%ibeam)
+    if (params%raytracing%ipol) then
+      write(u, fmt) "psi",  params%antenna%psi
+      write(u, fmt) "chi",  params%antenna%chi
+    end if
+    write(u, fmt) "filenm", quote(params%antenna%filenm)
+
+    write(u, '(/,a)') "[equilibrium]"
+    if (params%equilibrium%iequil /= defaults%equilibrium%iequil) &
+      write(u, fmt) "iequil", format_equil(params%equilibrium%iequil)
+    write(u, fmt) "filenm", quote(params%equilibrium%filenm)
+    if (params%equilibrium%icocos /= defaults%equilibrium%icocos) &
+      write(u, fmt) "icocos",  params%equilibrium%icocos
+    if (params%equilibrium%ipsinorm .neqv. defaults%equilibrium%ipsinorm) &
+      write(u, fmt) "ipsinorm", format_bool(params%equilibrium%ipsinorm)
+    if (params%equilibrium%idesc .neqv. defaults%equilibrium%idesc) &
+      write(u, fmt) "idesc", format_bool(params%equilibrium%idesc)
+    if (params%equilibrium%ifreefmt .neqv. defaults%equilibrium%ifreefmt) &
+      write(u, fmt) "ifreefmt", format_bool(params%equilibrium%ifreefmt)
+    if (params%equilibrium%ixp /= defaults%equilibrium%ixp) &
+      write(u, fmt) "ixp", format_x_point(params%equilibrium%ixp)
+    if (params%equilibrium%ssplps /= defaults%equilibrium%ssplps) &
+      write(u, fmt) "ssplps", params%equilibrium%ssplps
+    if (params%equilibrium%ssplf /= defaults%equilibrium%ssplf) &
+      write(u, fmt) "ssplf", params%equilibrium%ssplf
+    if (params%equilibrium%sgnb /= defaults%equilibrium%sgnb) &
+      write(u, fmt) "sgnb", params%equilibrium%sgnb
+    if (params%equilibrium%sgni /= defaults%equilibrium%sgni) &
+      write(u, fmt) "sgni", params%equilibrium%sgni
+    if (params%equilibrium%factb /= defaults%equilibrium%factb) &
+      write(u, fmt) "factb", params%equilibrium%factb
+
+    write(u, '(/,a)') "[profiles]"
+    write(u, fmt) "iprof", format_profiles(params%profiles%iprof)
+    write(u, fmt) "irho", format_rho(params%profiles%irho)
+    write(u, fmt) "filenm", quote(params%profiles%filenm)
+    if (params%profiles%sspld /= defaults%profiles%sspld) &
+      write(u, fmt) "sspld", params%profiles%sspld
+    if (params%profiles%factne /= defaults%profiles%factne) &
+      write(u, fmt) "factne", params%profiles%factne
+    if (params%profiles%factte /= defaults%profiles%factte) &
+      write(u, fmt) "factte", params%profiles%factte
+    if (params%profiles%iscal /= defaults%profiles%iscal) &
+      write(u, fmt) "iscal", format_scaling(params%profiles%iscal)
+    if (params%profiles%psnbnd /= defaults%profiles%psnbnd) &
+      write(u, fmt) "psnbnd", params%profiles%psnbnd
+
+    write(u, '(/,a)') "[output]"
+    if (params%output%ipec /= defaults%output%ipec) &
+      write(u, fmt) "ipec", format_rho(params%output%ipec)
+    if (params%output%nrho /= defaults%output%nrho) &
+      write(u, fmt) "nrho", params%output%nrho
+    if (params%output%istpr /= defaults%output%istpr) &
+      write(u, fmt) "istpr", params%output%istpr
+    if (params%output%istpl /= defaults%output%istpl) &
+      write(u, fmt) "istpl", params%output%istpl
+
+    write(u, '(/,a)') "[misc]"
+    write(u, fmt) "rwall", params%misc%rwall
+
+  end subroutine write_gray_config
+
+
+  ! Helper functions for formatting values
+
+  pure function format_bool(p) result(str)
+    logical, intent(in) :: p
+    character(len=:), allocatable :: str
+    str = trim(merge("true ", "false", p))
+  end function
+
+  pure function format_step(val) result(str)
+    integer(kind(step_enum)), intent(in) :: val
+    character(len=:), allocatable :: str
+    character(len=*), parameter :: choices(0:2) = &
+      [character(len=11) :: "ARCLEN", "TIME", "PHASE"]
+    str = "STEP_" // trim(choices(val))
+  end function
+
+  pure function format_absorp(val) result(str)
+    integer(kind(absorption_enum)), intent(in) :: val
+    character(len=:), allocatable :: str
+    character(len=*), parameter :: choices(0:3) = &
+      [character(len=8) :: "OFF", "WEAK", "FULL", "FULL_ALT"]
+    str = "ABSORP_" // trim(choices(val))
+  end function
+
+  pure function format_current(val) result(str)
+    integer(kind(current_drive_enum)), intent(in) :: val
+    character(len=:), allocatable :: str
+    character(len=*), parameter :: choices(0:3) = &
+      [character(len=10) :: "OFF", "COHEN", "NO_TRAP", "NEOCLASSIC"]
+    str = "CD_" // trim(choices(val))
+  end function
+
+  pure function format_polar(val) result(str)
+    integer(kind(polar_enum)), intent(in) :: val
+    character(len=:), allocatable :: str
+    str = merge("MODE_O", "MODE_X", val == 1)
+  end function
+
+  pure function format_beam(val) result(str)
+    integer(kind(beam_enum)), intent(in) :: val
+    character(len=:), allocatable :: str
+    character(len=*), parameter :: choices(0:2) = ["0D", "1D", "2D"]
+    str = "BEAM_" // choices(val)
+  end function
+
+  pure function format_equil(val) result(str)
+    integer(kind(equil_enum)), intent(in) :: val
+    character(len=:), allocatable :: str
+    character(len=*), parameter :: choices(0:3) = &
+      [character(len=13) :: "VACUUM", "ANALYTICAL", &
+       "EQDSK_FULL", "EQDSK_PARTIAL"]
+    str = "EQ_" // trim(choices(val))
+  end function
+
+  pure function format_x_point(val) result(str)
+    integer(kind(x_point_enum)), intent(in) :: val
+    character(len=:), allocatable :: str
+    character(len=*), parameter :: choices(-1:+1) = &
+      [character(len=10) :: "AT_BOTTOM", "IS_MISSING", "AT_TOP"]
+    str = "X_" // trim(choices(val))
+  end function
+
+  pure function format_scaling(val) result(str)
+    integer(kind(scaling_enum)), intent(in) :: val
+    character(len=:), allocatable :: str
+    character(len=*), parameter :: choices(0:2) = &
+      [character(len=9) :: "COLLISION", "GREENWALD", "OFF"]
+    str = "SCALE_" // trim(choices(val))
+  end function
+
+  pure function format_rho(val) result(str)
+    integer(kind(rho_enum)), intent(in) :: val
+    character(len=:), allocatable :: str
+    character(len=*), parameter :: choices(0:2) = ["TOR", "POL", "PSI"]
+    str = "RHO_" // trim(choices(val))
+  end function
+
+  pure function format_profiles(val) result(str)
+    integer(kind(profiles_enum)), intent(in) :: val
+    character(len=:), allocatable :: str
+    str = "PROF_" // trim(merge("ANALYTIC", "NUMERIC ", val == 0))
+  end function
+
+  pure function quote(str) result(quoted)
+    character(*), intent(in) :: str
+    character(len=:), allocatable :: quoted
+    quoted = '"' // trim(str) // '"'
+  end function
+
+end program