diff --git a/matlab/+sonpipe/channelinfo.m b/matlab/+sonpipe/channelinfo.m
index c59fddb..44a07d7 100644
--- a/matlab/+sonpipe/channelinfo.m
+++ b/matlab/+sonpipe/channelinfo.m
@@ -9,6 +9,11 @@
 %
 %   See also sonpipe.read_SOMSMR_header
 
+	arguments
+		header
+		channel_number {mustBeNumeric}
+	end
+
 	if isempty(header) || ~isfield(header, 'channelinfo') || isempty(header.channelinfo)
 		error('sonpipe:noChannels', 'The header contains no channels.');
 	end
diff --git a/matlab/+sonpipe/channels.m b/matlab/+sonpipe/channels.m
index f519e29..7fcf3dd 100644
--- a/matlab/+sonpipe/channels.m
+++ b/matlab/+sonpipe/channels.m
@@ -17,7 +17,12 @@
 %
 %   See also sonpipe.read_SOMSMR_header
 
-	if nargin < 2 || isempty(header)
+	arguments
+		filename {mustBeTextScalar}
+		header = []            % [] or a header struct; read from FILENAME if omitted
+	end
+
+	if isempty(header)
 		header = sonpipe.read_SOMSMR_header(filename);
 	end
 
diff --git a/matlab/+sonpipe/executable.m b/matlab/+sonpipe/executable.m
index 649e798..27b37d3 100644
--- a/matlab/+sonpipe/executable.m
+++ b/matlab/+sonpipe/executable.m
@@ -17,13 +17,22 @@
 %   Lookup order when no value is cached:
 %     1. the SONPIPE environment variable, if set
 %     2. 'sonpipe' on the system PATH
-%     3. 'python3 -m sonpipe'
-%     4. 'python -m sonpipe'
+%     3. sonpipe at the default install locations (~/.local/bin/sonpipe, the
+%        install.sh venv, and the Windows %LOCALAPPDATA% venv). These are
+%        probed by absolute path because a MATLAB GUI on macOS/Windows does not
+%        inherit the interactive shell PATH, so a working ~/.local/bin install
+%        is otherwise invisible to step 2.
+%     4. 'python3 -m sonpipe'
+%     5. 'python -m sonpipe'
 %
 %   Each candidate is verified by running "<candidate> --version".
 %
 %   See also sonpipe.read_SOMSMR_header
 
+	arguments
+		newvalue = ''   % command string; nargin distinguishes query() from set('')
+	end
+
 	persistent CACHED
 
 	if nargin >= 1
@@ -43,6 +52,7 @@
 		candidates{end+1} = envval;
 	end
 	candidates{end+1} = 'sonpipe';
+	candidates = [candidates, defaultInstallCandidates()];
 	candidates{end+1} = 'python3 -m sonpipe';
 	candidates{end+1} = 'python -m sonpipe';
 
@@ -60,3 +70,25 @@
 		 '''pip install sonpipe'', or point MATLAB at it with ' ...
 		 'sonpipe.executable(PATH) or the SONPIPE environment variable.']);
 end
+
+function c = defaultInstallCandidates()
+% Absolute paths where install.sh / install.ps1 place sonpipe. Only paths that
+% exist on disk are returned (each is quoted so spaces in the path are safe).
+	c = {};
+	paths = {};
+	home = getenv('HOME');
+	if isempty(home), home = getenv('USERPROFILE'); end
+	if ~isempty(home)
+		paths{end+1} = fullfile(home, '.local', 'bin', 'sonpipe');
+		paths{end+1} = fullfile(home, '.local', 'share', 'sonpipe', 'venv', 'bin', 'sonpipe');
+	end
+	lad = getenv('LOCALAPPDATA');
+	if ~isempty(lad)
+		paths{end+1} = fullfile(lad, 'sonpipe', 'venv', 'Scripts', 'sonpipe.exe');
+	end
+	for i = 1:numel(paths)
+		if isfile(paths{i})
+			c{end+1} = ['"' paths{i} '"']; %#ok<AGROW>
+		end
+	end
+end
diff --git a/matlab/+sonpipe/private/invoke_binary.m b/matlab/+sonpipe/private/invoke_binary.m
index 39d40c5..b30901d 100644
--- a/matlab/+sonpipe/private/invoke_binary.m
+++ b/matlab/+sonpipe/private/invoke_binary.m
@@ -15,6 +15,11 @@
 %
 %   This is a private helper for the +sonpipe package.
 
+	arguments
+		args      {mustBeTextScalar}
+		precision {mustBeTextScalar}
+	end
+
 	exe = sonpipe.executable();
 	tmp = [tempname() '.bin'];
 	cleaner = onCleanup(@() deletefile(tmp));
diff --git a/matlab/+sonpipe/private/invoke_text.m b/matlab/+sonpipe/private/invoke_text.m
index 47238ce..1950c44 100644
--- a/matlab/+sonpipe/private/invoke_text.m
+++ b/matlab/+sonpipe/private/invoke_text.m
@@ -9,6 +9,10 @@
 %
 %   This is a private helper for the +sonpipe package.
 
+	arguments
+		args {mustBeTextScalar}
+	end
+
 	exe = sonpipe.executable();
 	cmd = [exe ' ' args];
 	[status, txt] = sonpipe.runcmd(cmd);
diff --git a/matlab/+sonpipe/read_SOMSMR_datafile.m b/matlab/+sonpipe/read_SOMSMR_datafile.m
index 134f77a..d6f0851 100644
--- a/matlab/+sonpipe/read_SOMSMR_datafile.m
+++ b/matlab/+sonpipe/read_SOMSMR_datafile.m
@@ -32,6 +32,14 @@
 %
 %   See also sonpipe.read_SOMSMR_header, sonpipe.read_SOMSMR_sampleinterval
 
+	arguments
+		filename       {mustBeTextScalar}
+		header                                       % [] or a header struct
+		channel_number {mustBeNumeric}
+		t0 (1,1)       {mustBeNumeric}
+		t1 (1,1)       {mustBeNumeric}
+	end
+
 	data = [];
 	total_samples = [];
 	total_time = [];
diff --git a/matlab/+sonpipe/read_SOMSMR_header.m b/matlab/+sonpipe/read_SOMSMR_header.m
index d11f217..f835a71 100644
--- a/matlab/+sonpipe/read_SOMSMR_header.m
+++ b/matlab/+sonpipe/read_SOMSMR_header.m
@@ -37,6 +37,10 @@
 %
 %   See also sonpipe.read_SOMSMR_datafile, sonpipe.read_SOMSMR_sampleinterval
 
+	arguments
+		filename {mustBeTextScalar}
+	end
+
 	txt = invoke_text(sprintf('header "%s"', filename));
 	raw = jsondecode(txt);
 
diff --git a/matlab/+sonpipe/read_SOMSMR_sampleinterval.m b/matlab/+sonpipe/read_SOMSMR_sampleinterval.m
index 9f999ce..e5ebfb4 100644
--- a/matlab/+sonpipe/read_SOMSMR_sampleinterval.m
+++ b/matlab/+sonpipe/read_SOMSMR_sampleinterval.m
@@ -18,6 +18,12 @@
 %
 %   See also sonpipe.read_SOMSMR_header, sonpipe.read_SOMSMR_datafile
 
+	arguments
+		filename       {mustBeTextScalar}
+		header                                       % [] or a header struct (unused)
+		channel_number {mustBeNumeric}
+	end
+
 	txt = invoke_text(sprintf('sampleinterval "%s" -c %d', filename, channel_number));
 	r = jsondecode(txt);
 
diff --git a/matlab/+sonpipe/runcmd.m b/matlab/+sonpipe/runcmd.m
index ce55a3d..88ff67f 100644
--- a/matlab/+sonpipe/runcmd.m
+++ b/matlab/+sonpipe/runcmd.m
@@ -14,6 +14,10 @@
 %
 %   See also sonpipe.executable
 
+	arguments
+		cmd {mustBeTextScalar}
+	end
+
 	if ispc
 		[status, out] = system(cmd);
 		return;