diff --git a/editorconfig/line_checkers.go b/editorconfig/line_checkers.go
new file mode 100644
index 0000000..b14848c
--- /dev/null
+++ b/editorconfig/line_checkers.go
@@ -0,0 +1,144 @@
+package editorconfig
+
+import (
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+// tab_width, charset, end_of_line, insert_final_newline and root do not have any affect on our line
+// checkers (they apply to the full files, not lines).
+
+var lineCheckers = map[string]LineChecker{
+	"indent_style":             CheckIndentStyleRule,
+	"indent_size":              CheckIndentSizeRule,
+	"trim_trailing_whitespace": CheckTrimTrailingWhitespaceRule,
+}
+
+type LineChecker func(ruleValue string, line string) *LineCheckResult
+
+// @todo - add fixers to each instance of LineCheckResult.
+type LineCheckResult struct {
+	isOk           bool
+	messageIfNotOk string
+}
+
+var hasIndentationRegexp = regexp.MustCompile(`^[\t ]`)
+var hasNoIndentationRegexp = regexp.MustCompile(`^([^\t ]|$)`)
+var indentedWithMixedTabsAndSpacesRegexp = regexp.MustCompile(`^(\t+ +| +\t+)`)
+var indentedWithTabsRegexp = regexp.MustCompile(`^\t+`)
+var indentedWithTabsThenCommentLineRegexp = regexp.MustCompile(`^\t+ \*`)
+var indentedWithSpacesRegexp = regexp.MustCompile(`^ +`)
+
+func HasIndentation(s string) bool {
+	return hasIndentationRegexp.MatchString(s)
+}
+
+func HasNoIndentation(s string) bool {
+	return hasNoIndentationRegexp.MatchString(s)
+}
+
+func IsIndentedWithMixedTabsAndSpaces(s string) bool {
+	return indentedWithMixedTabsAndSpacesRegexp.MatchString(s)
+}
+
+func IsIndentedWithTabs(s string) bool {
+	return indentedWithTabsRegexp.MatchString(s)
+}
+
+// This allows comments like /**\n\t *\n\t */
+func IsIndentedWithTabsThenCommentLine(s string) bool {
+	return indentedWithTabsThenCommentLineRegexp.MatchString(s)
+}
+
+func IsIndentedWithSpaces(s string) bool {
+	return indentedWithSpacesRegexp.MatchString(s)
+}
+
+func CheckIndentStyleRule(ruleValue string, line string) *LineCheckResult {
+	if HasNoIndentation(line) {
+		return &LineCheckResult{isOk: true}
+	}
+
+	if strings.ToLower(ruleValue) == "tab" {
+		if IsIndentedWithSpaces(line) {
+			return &LineCheckResult{isOk: false, messageIfNotOk: "starts with space instead of tab"}
+		} else if IsIndentedWithMixedTabsAndSpaces(line) && !IsIndentedWithTabsThenCommentLine(line) {
+			return &LineCheckResult{isOk: false, messageIfNotOk: "indented with mix of tabs and spaces instead of just tabs"}
+		} else {
+			return &LineCheckResult{isOk: true}
+		}
+	}
+
+	if strings.ToLower(ruleValue) == "space" {
+		if IsIndentedWithTabs(line) {
+			return &LineCheckResult{isOk: false, messageIfNotOk: "starts with tab instead of space"}
+		} else if IsIndentedWithMixedTabsAndSpaces(line) {
+			return &LineCheckResult{isOk: false, messageIfNotOk: "indented with mix of tabs and spaces instead of just tabs"}
+		} else {
+			return &LineCheckResult{isOk: true}
+		}
+	}
+
+	return &LineCheckResult{isOk: false, messageIfNotOk: "invalid value for indent_style: " + ruleValue}
+}
+
+func CheckIndentSizeRule(ruleValue string, line string) *LineCheckResult {
+	if ruleValue == "tab" {
+		return &LineCheckResult{isOk: true}
+	}
+
+	if HasNoIndentation(line) {
+		return &LineCheckResult{isOk: true}
+	}
+
+	ruleValueInt, err := strconv.Atoi(ruleValue)
+	if err != nil {
+		return &LineCheckResult{isOk: false, messageIfNotOk: "value is not an integer: " + ruleValue}
+	}
+
+	if ruleValueInt < 1 {
+		return &LineCheckResult{isOk: false, messageIfNotOk: "number of spaces must be 1 or more, is: " + ruleValue}
+	}
+
+	if strings.HasPrefix(line, "\t") {
+		return &LineCheckResult{isOk: false, messageIfNotOk: "should be indented with spaces but is indented with tabs"}
+	}
+
+	// Indented with spaces. Ensure the number of spaces is divisible by the rule value, but also
+	// allow an extra space followed by * to allow for comments like /**\n   *\n   */ (note the
+	// extra space before the * on the 2nd and 3rd lines).
+	trimmedLine := line
+	for strings.HasPrefix(trimmedLine, strings.Repeat(" ", ruleValueInt)) {
+		trimmedLine = (trimmedLine)[ruleValueInt:]
+	}
+	if strings.HasPrefix(trimmedLine, " *") {
+		return &LineCheckResult{isOk: true}
+	}
+	if IsIndentedWithTabs(trimmedLine) {
+		return &LineCheckResult{isOk: false, messageIfNotOk: "indented with mix of spaces and tabs instead of just spaces"}
+	}
+	if HasIndentation(trimmedLine) {
+		leftSpaces := len(line) - len(strings.TrimLeft(line, " "))
+		return &LineCheckResult{isOk: false, messageIfNotOk: "starts with " + strconv.Itoa(leftSpaces) + " spaces which does not divide by " + ruleValue}
+	}
+
+	return &LineCheckResult{isOk: true}
+}
+
+func CheckTrimTrailingWhitespaceRule(ruleValue string, line string) *LineCheckResult {
+	if strings.ToLower(ruleValue) == "false" {
+		return &LineCheckResult{isOk: true}
+	}
+
+	if strings.ToLower(ruleValue) != "true" {
+		return &LineCheckResult{isOk: false, messageIfNotOk: "value must be true or false, but is: " + ruleValue}
+	}
+
+	trimmed := strings.TrimRight(line, " \t")
+	if len(line) != len(trimmed) {
+		return &LineCheckResult{isOk: false, messageIfNotOk: "line has trailing whitespace"}
+	}
+
+	return &LineCheckResult{isOk: true}
+}
diff --git a/editorconfig/line_checkers_test.go b/editorconfig/line_checkers_test.go
new file mode 100644
index 0000000..e08c607
--- /dev/null
+++ b/editorconfig/line_checkers_test.go
@@ -0,0 +1,105 @@
+package editorconfig
+
+import (
+	"testing"
+)
+
+func ExpectPass(line string, ruleValue string, lineChecker LineChecker, t *testing.T) {
+	result := lineChecker(ruleValue, line)
+	if !result.isOk {
+		t.Error("Expected line to pass, but it failed: \"" + line + "\" for rule value \"" + ruleValue + "\", had error message: " + result.messageIfNotOk)
+	}
+}
+
+func ExpectFail(line string, ruleValue string, lineChecker LineChecker, t *testing.T, expectedError string) {
+	result := lineChecker(ruleValue, line)
+	if result.isOk {
+		t.Error("Expected line to fail, but it passed: \"" + line + "\" for rule value \"" + ruleValue + "\"")
+		return
+	}
+
+	if !result.isOk && result.messageIfNotOk != expectedError {
+		t.Error("Line \"" + line + "\" failed with error message \"" + result.messageIfNotOk + "\" but had expected \"" + expectedError + "\"")
+		return
+	}
+}
+
+func TestCheckIndentStyleRule(t *testing.T) {
+	f := CheckIndentStyleRule
+
+	ExpectPass("", "space", f, t)
+	ExpectPass("line", "space", f, t)
+	ExpectPass(" line", "space", f, t)
+	ExpectPass(" ", "space", f, t)
+	ExpectPass("  line", "space", f, t)
+	ExpectFail(" \tline", "space", f, t, "indented with mix of tabs and spaces instead of just tabs")
+	ExpectFail("\tline", "space", f, t, "starts with tab instead of space")
+	ExpectFail("\t line", "space", f, t, "starts with tab instead of space")
+
+	ExpectPass("", "tab", f, t)
+	ExpectPass("line", "tab", f, t)
+	ExpectPass("\n", "tab", f, t)
+	ExpectPass("\tline", "tab", f, t)
+	ExpectPass("\t\tline", "tab", f, t)
+	ExpectFail(" \tline", "tab", f, t, "starts with space instead of tab")
+	ExpectFail("\t line", "tab", f, t, "indented with mix of tabs and spaces instead of just tabs")
+	ExpectFail("\t ", "tab", f, t, "indented with mix of tabs and spaces instead of just tabs")
+
+	// Allow comments like /**\n\t *\n\t */
+	ExpectPass("\t *line", "tab", f, t)
+
+	ExpectFail("  line", "dinosaurs", f, t, "invalid value for indent_style: dinosaurs")
+}
+
+func TestCheckIndentSizeRule(t *testing.T) {
+	f := CheckIndentSizeRule
+
+	// 'indent_size=tab' can never fail this rule.
+	ExpectPass("line", "tab", f, t)
+	ExpectPass(" line", "tab", f, t)
+	ExpectPass("  line", "tab", f, t)
+
+	ExpectPass("", "2", f, t)
+	ExpectPass("line", "2", f, t)
+	ExpectPass("  line", "2", f, t)
+	ExpectPass("    line", "2", f, t)
+	ExpectPass("      line", "2", f, t)
+	ExpectFail(" line", "2", f, t, "starts with 1 spaces which does not divide by 2")
+	ExpectFail("   line", "2", f, t, "starts with 3 spaces which does not divide by 2")
+	ExpectFail("     line", "2", f, t, "starts with 5 spaces which does not divide by 2")
+	ExpectFail("\tline", "2", f, t, "should be indented with spaces but is indented with tabs")
+	ExpectFail("\t\tline", "2", f, t, "should be indented with spaces but is indented with tabs")
+	ExpectFail("  \tline", "2", f, t, "indented with mix of spaces and tabs instead of just spaces")
+
+	// Allow comments like /**\n   *\n   */ (note the extra space before the * on the 2nd and 3rd lines)
+	ExpectPass("   * line", "2", f, t)
+	ExpectFail("   ^ line", "2", f, t, "starts with 3 spaces which does not divide by 2")
+
+	ExpectPass("", "3", f, t)
+	ExpectPass("line", "3", f, t)
+	ExpectPass("      line", "3", f, t)
+	ExpectFail("     line", "3", f, t, "starts with 5 spaces which does not divide by 3")
+
+	ExpectFail(" anything", "0", f, t, "number of spaces must be 1 or more, is: 0")
+	ExpectFail(" anything", "-1", f, t, "number of spaces must be 1 or more, is: -1")
+	ExpectFail(" anything", "asd", f, t, "value is not an integer: asd")
+}
+
+func TestCheckTrimTrailingWhitespaceRule(t *testing.T) {
+	f := CheckTrimTrailingWhitespaceRule
+
+	// 'trim_trailing_whitespace=false' can never fail this rule.
+	ExpectPass("line", "false", f, t)
+	ExpectPass("line ", "false", f, t)
+	ExpectPass("line\t", "false", f, t)
+	ExpectPass("line \t \t \t", "false", f, t)
+
+	ExpectPass("line", "true", f, t)
+	ExpectPass("line line", "true", f, t)
+	ExpectPass("line line", "true", f, t)
+
+	ExpectFail("line line ", "true", f, t, "line has trailing whitespace")
+	ExpectFail("line line\t", "true", f, t, "line has trailing whitespace")
+	ExpectFail("line line   ", "true", f, t, "line has trailing whitespace")
+	ExpectFail("line line   \t", "true", f, t, "line has trailing whitespace")
+}