diff --git a/src/Trajectory.jl b/src/Trajectory.jl
index ae2c2aae..ee9e70d8 100644
--- a/src/Trajectory.jl
+++ b/src/Trajectory.jl
@@ -3,8 +3,7 @@
 
 Trajectory constructor data type. 
 
-Defaults to reading with the Chemfiles infrastructure, except for DCD and PDB trajectory
-files, if the "PDBTraj" option is provided.
+Defaults to reading with the Chemfiles infrastructure, except for DCD and PDB trajectory files, if the "PDBTraj" option is provided.
 
 See memory issue (https://github.com/chemfiles/Chemfiles.jl/issues/44)
 
@@ -21,6 +20,9 @@ end
 stream(traj::Trajectory) = traj.stream.st
 set_stream!(traj::Trajectory, st) = traj.stream.st = st
 
+# Trajectory formats
+const trajectory_formats = String[]
+
 # Include specific predefined trajectory types
 include("./trajectory_formats/ChemFiles.jl")
 include("./trajectory_formats/NamdDCD.jl")
@@ -33,20 +35,28 @@ function Trajectory(
     format::String="",
     chemfiles=false,
 )
+    if !isempty(format) && !(format in trajectory_formats)
+        throw(ArgumentError("""\n
+            Trajectory format not properly set: $format 
+            Available trajectory formats: $(join(trajectory_formats, ", "))
+
+        """))
+    end
     filename = expanduser(filename) # expand tilde on Unix systems, to username
-    if !chemfiles && (format == "dcd" || split(filename, '.')[end] == "dcd")
-        trajectory = NamdDCD(filename, solute, solvent)
-    elseif !chemfiles && format == "PDBTraj"
-        trajectory = PDBTraj(filename, solute, solvent)
+    file_extension = filename[findlast(==('.'), filename)+1:end]
+    trajectory = if !chemfiles && (format == "dcd" || file_extension == "dcd")
+        NamdDCD(filename, solute, solvent)
+    elseif !chemfiles && (format == "PDBTraj" || file_extension =="pdb")
+        PDBTraj(filename, solute, solvent)
     else
-        trajectory = ChemFile(filename, solute, solvent, format=format)
+        ChemFile(filename, solute, solvent, format=format)
     end
     return trajectory
 end
 
 # If only one selection is provided, assume that the solute and the solvent are the same
 Trajectory(filename::String, solvent::AtomSelection; format::String="", chemfiles=false) =
-    Trajectory(filename, solvent, solvent, format=format, chemfiles=chemfiles)
+    Trajectory(filename, solvent, solvent; format, chemfiles)
 
 #=
     convert_unitcell(unitcell::Union{SVector{3}, SMatrix{3,3}})
@@ -108,6 +118,9 @@ end
     protein = AtomSelection(select(atoms, "protein"), nmols=1)
     tmao = AtomSelection(select(atoms, "resname TMAO"), natomspermol=14)
 
+    # Throw if trajectory type is not available
+    @test_throws ArgumentError Trajectory("$(Testing.data_dir)/PDB/trajectory.pdb", protein, tmao; format="XXX")
+
     # NAMD DCD file
     traj = Trajectory("$(Testing.data_dir)/NAMD/trajectory.dcd", protein, tmao)
     @test traj.nframes == 20
@@ -124,6 +137,9 @@ end
     @test ComplexMixtures.natoms(traj.solute) == 1463
     @test ComplexMixtures.natoms(traj.solvent) == 2534
     @test ComplexMixtures.convert_unitcell(ComplexMixtures.getunitcell(traj)) ≈ SVector(84.47962951660156, 84.47962951660156, 84.47962951660156)
+    # Test determining format from file extension
+    traj = Trajectory("$(Testing.data_dir)/PDB/trajectory.pdb", protein, tmao)
+    @test ComplexMixtures.natoms(traj.solute) == 1463
 
     # Chemfiles with NAMD
     traj = Trajectory(
diff --git a/src/mddf.jl b/src/mddf.jl
index bef36c38..3d4d5c1f 100644
--- a/src/mddf.jl
+++ b/src/mddf.jl
@@ -183,7 +183,7 @@ function mddf(
     trajectory_file::String,
     solute::AtomSelection,
     solvent::AtomSelection,
-    options::Options;
+    options::Options=Options();
     trajectory_format::String="",
     chemfiles::Bool=false,
     kargs...)
@@ -194,7 +194,7 @@ end
 function mddf(
     trajectory_file::String,
     solute_and_solvent::AtomSelection,
-    options::Options;
+    options::Options=Options();
     trajectory_format::String="",
     chemfiles::Bool=false,
     kargs...
@@ -528,7 +528,7 @@ function coordination_number(
     trajectory_file::String,
     solute::AtomSelection,
     solvent::AtomSelection,
-    options::Options;
+    options::Options=Options();
     trajectory_format::String="",
     chemfiles::Bool=false,
     kargs...)
@@ -540,7 +540,7 @@ end
 function coordination_number(
     trajectory_file::String,
     solute_and_solvent::AtomSelection,
-    options::Options;
+    options::Options=Options();
     trajectory_format::String="",
     chemfiles::Bool=false,
     kargs...
@@ -608,9 +608,6 @@ end
     # Test wrong frame_weights input
     @test_throws ArgumentError mddf(trajectory_file, protein, water, Options(); frame_weights=[1.0], trajectory_format)
 
-    # The coordination_number(::String, args...; kargs...) is a placeholder for the docs only
-    @test_throws ArgumentError coordination_number("string.txt", 1.0)
-
     # Self correlation
     atoms = readPDB("$data_dir/toy/self_monoatomic.pdb")
     atom = AtomSelection(select(atoms, "resname WAT and model 1"), natomspermol=1)
@@ -709,6 +706,38 @@ end
         @test R.density.solvent ≈ 2 / R.volume.total
         @test R.density.solvent_bulk ≈ 0.5 / R.volume.bulk
     end
+end
+
+@testitem "mddf - available methods" begin
+    using ComplexMixtures
+    using PDBTools: readPDB, select
+    using ComplexMixtures.Testing: data_dir
+    atoms = readPDB("$data_dir/toy/cross.pdb")
+    protein = AtomSelection(select(atoms, "protein and model 1"), nmols=1)
+    water = AtomSelection(select(atoms, "resname WAT and model 1"), natomspermol=3)
+    trajectory_file = "$data_dir/toy/cross.pdb"
+    
+    atom = AtomSelection(select(atoms, "resname WAT and model 1"), natomspermol=1)
+    t = Trajectory(trajectory_file, atom; format="PDBTraj")
+
+    options = Options()
+    trajectory_file = "$data_dir/toy/self_monoatomic.pdb"
+    atom = AtomSelection(select(atoms, "resname WAT and model 1"), natomspermol=1)
+    r1 = mddf(trajectory_file, atom, atom)
+    r2 = mddf(trajectory_file, atom, atom, Options())
+    @test coordination_number(r1) ≈ coordination_number(r2)
+    r1 = mddf(trajectory_file, atom)
+    r2 = mddf(trajectory_file, atom, Options())
+    @test coordination_number(r1) ≈ coordination_number(r2)
+    r1 = coordination_number(trajectory_file, atom, atom)
+    r2 = coordination_number(trajectory_file, atom, atom, Options())
+    @test coordination_number(r1) ≈ coordination_number(r2)
+    r1 = coordination_number(trajectory_file, atom)
+    r2 = coordination_number(trajectory_file, atom, Options())
+    @test coordination_number(r1) ≈ coordination_number(r2)
+
+    # The coordination_number(::String, args...; kargs...) is a placeholder for the docs only
+    @test_throws ArgumentError coordination_number("string.txt", 1.0)
 
 end
 
diff --git a/src/trajectory_formats/ChemFiles.jl b/src/trajectory_formats/ChemFiles.jl
index 8e9097fb..482ae46c 100644
--- a/src/trajectory_formats/ChemFiles.jl
+++ b/src/trajectory_formats/ChemFiles.jl
@@ -5,6 +5,9 @@
 #
 import Chemfiles
 
+# Add this format to list of available formats 
+push!(trajectory_formats, "Chemfiles")
+
 #"""
 #
 #$(TYPEDEF)
diff --git a/src/trajectory_formats/NamdDCD.jl b/src/trajectory_formats/NamdDCD.jl
index 726f648b..555bc243 100644
--- a/src/trajectory_formats/NamdDCD.jl
+++ b/src/trajectory_formats/NamdDCD.jl
@@ -1,3 +1,6 @@
+# Add this format to list of available formats
+push!(trajectory_formats, "dcd")
+
 #
 # Structure to contain DCD trajectories produces with Namd. 
 #
diff --git a/src/trajectory_formats/PDBTraj.jl b/src/trajectory_formats/PDBTraj.jl
index d0cfaed9..e44aa7a1 100644
--- a/src/trajectory_formats/PDBTraj.jl
+++ b/src/trajectory_formats/PDBTraj.jl
@@ -1,3 +1,6 @@
+# Add this format to list of available files
+push!(trajectory_formats, "PDBTraj")
+
 #"""
 #
 #$(TYPEDEF)