diff --git a/scripts/psalm.js b/scripts/psalm.js
new file mode 100644
index 0000000..2d65424
--- /dev/null
+++ b/scripts/psalm.js
@@ -0,0 +1,12 @@
+const psalm = require( '../src/linters/psalm' );
+
+const standardDir = process.argv[2];
+const codedir = process.argv[3];
+
+psalm( standardDir )( codedir )
+	.then( results => {
+		console.log( results );
+	})
+	.catch( err => {
+		console.error( `error: ${err.message}` )
+	})
diff --git a/src/linters/psalm/index.js b/src/linters/psalm/index.js
new file mode 100644
index 0000000..256382c
--- /dev/null
+++ b/src/linters/psalm/index.js
@@ -0,0 +1,128 @@
+const child_process = require( 'child_process' );
+const fs = require( 'fs' );
+const path = require( 'path' );
+
+const CONFIG_NAMES = [
+	'psalm.xml',
+];
+
+/**
+ * Convert a Psalm error into formatOutput-style results.
+ *
+ * @param {Object} message Issue data from Psalm.
+ * @returns {Object}
+ */
+const formatMessage = message => {
+	const text = `${message.message}`;
+
+	return {
+		line:     message.line_from,
+		column:   0,
+		severity: message.severity,
+		message:  message.message,
+		source:   message.type,
+	};
+};
+
+/**
+ * Convert Psalm results into common output format.
+ *
+ * @param {Array} data     Warnings and errors from Psalm.
+ * @param {String} codepath Path to the code getting linted.
+ * @returns {{files, totals: {warnings: *, errors: *}}}
+ */
+const formatOutput = ( data, codepath ) => {
+	const totals = {
+		errors: 0,
+		warnings: 0,
+	};
+	const files = {};
+	data.forEach( psalmIssue => {
+		const relPath = path.relative( codepath, psalmIssue.file_path );
+		if ( psalmIssue.severity === 'error' ) {
+			totals.errors++;
+		} else if ( psalmIssue.severity === 'warning' ) {
+			totals.warnings++;
+		}
+		files[ relPath ] = formatMessage( psalmIssue )
+	} );
+
+	return { totals, files };
+};
+
+/**
+ * Run Psalm typechecking.
+ *
+ * @param {String} standardPath Path to custom standard set.
+ */
+module.exports = standardPath => codepath => {
+	const psalmPath = path.join( standardPath, 'vendor', 'bin', 'psalm' );
+
+	const args = [
+		psalmPath,
+		'--output-format=json',
+		'--no-progress',
+	];
+	const opts = {
+		cwd: codepath,
+		env: process.env,
+	};
+
+	return composerInstall( codepath ).then( () => {
+		return new Promise( ( resolve, reject ) => {
+			console.log( 'Spawning PHP process', psalmPath, args, opts );
+			const proc = child_process.spawn( 'php', args, opts );
+			let stdout = '';
+			let stderr = '';
+			proc.stdout.on( 'data', data => stdout += data );
+			proc.stderr.on( 'data', data => stderr += data );
+			proc.on( 'error', e => { console.log( e ) } );
+			proc.on( 'close', errCode => {
+				// Error codes:
+				// 0: no errors found
+				// 1: errors found or Psalm processing error
+				let data;
+				try {
+					data = JSON.parse( stdout );
+				} catch ( e ) {
+					// Couldn't decode JSON, so likely a human readable error.
+					console.log( stdout )
+					console.log( stderr )
+					console.log( e )
+					return reject( stdout + stderr );
+				}
+
+				resolve( formatOutput( data, codepath ) );
+			} );
+		} );
+	} );
+};
+
+function composerInstall( codepath ) {
+	const opts = {
+		cwd: codepath,
+		env: process.env,
+	};
+	return new Promise( ( resolve, reject ) => {
+		const proc = child_process.spawn( 'composer', [ 'install', '--no-dev' ], opts );
+		let stdout = '';
+		let stderr = '';
+		proc.stdout.on( 'data', data => {
+			stdout += data;
+			console.log( data );
+		} );
+		proc.stderr.on( 'data', data => {
+			stderr += data;
+			console.error( String( data ) );
+		 } );
+		proc.on( 'error', e => { console.log( e ) } );
+		proc.on( 'close', errCode => {
+			if ( errCode > 0 ) {
+				reject( stderr )
+			}
+
+			resolve( stdout );
+		} );
+	} );
+}
+