diff --git a/README.md b/README.md
index 8bb9642..8034037 100644
--- a/README.md
+++ b/README.md
@@ -51,6 +51,34 @@ Refer to the [basic example](examples/basic/main.go) for API usage.
 
 For more details, please check the [documentation](https://docs.qasphere.com/).
 
+## Custom Fields
+
+Custom fields must be declared with `AddCustomField`/`AddCustomFields` before adding test cases that use them. Three types are supported:
+
+- `text` — plain text, no length limit.
+- `dropdown` — the value must match one of the options defined for the field in QA Sphere (option values are limited to 255 characters).
+- `richtext` — rich text, no length limit. **Values are HTML** (e.g. `<p>…</p>`, `<pre><code>…</code></pre>`), unlike `Preconditions` and `Steps`, which take markdown. QA Sphere sanitizes the HTML on import using an allowlist of tags and attributes.
+
+For example, to populate QA Sphere's rich text Description field:
+
+```go
+qasCSV := qascsv.NewQASphereCSV()
+_ = qasCSV.AddCustomField(qascsv.CustomField{
+	SystemName: "description",
+	Type:       qascsv.CustomFieldTypeRichtext,
+})
+_ = qasCSV.AddTestCase(qascsv.TestCase{
+	Title:      "Login with valid credentials",
+	FolderPath: []string{"Auth"},
+	Priority:   qascsv.PriorityHigh,
+	CustomFields: map[string]qascsv.CustomFieldValue{
+		"description": {Value: "<p>Verifies the standard login flow.</p>"},
+	},
+})
+```
+
+This produces a `custom_field_richtext_description` column matching QA Sphere's CSV export format.
+
 ## Contributing
 
 We welcome contributions! If you have a feature request, encounter a problem, or have questions, please [create a new issue](https://github.com/Hypersequent/qasphere-csv/issues/new/choose). You can also contribute by opening a pull request.
diff --git a/qacsv_test.go b/qacsv_test.go
index 35fab5a..62d7844 100644
--- a/qacsv_test.go
+++ b/qacsv_test.go
@@ -1,6 +1,8 @@
 package qascsv
 
 import (
+	"encoding/csv"
+	"encoding/json"
 	"io"
 	"os"
 	"strings"
@@ -373,12 +375,12 @@ var customFieldFailureTestCases = []TestCase{
 		},
 	},
 	{
-		Title:      "tc-with-very-long-custom-field-value",
+		Title:      "tc-with-very-long-dropdown-value",
 		FolderPath: []string{"custom-fields-errors"},
 		Priority:   "medium",
 		CustomFields: map[string]CustomFieldValue{
-			"notes": {
-				Value: strings.Repeat("a", 256), // Exceeds 255 char limit
+			"test_env": {
+				Value: strings.Repeat("a", 256), // Dropdown options are limited to 255 chars
 			},
 		},
 	},
@@ -457,6 +459,64 @@ func TestCustomFieldFailureTestCases(t *testing.T) {
 	}
 }
 
+func TestRichtextCustomField(t *testing.T) {
+	qasCSV := NewQASphereCSV()
+	require.NoError(t, qasCSV.AddCustomField(CustomField{
+		SystemName: "description",
+		Type:       CustomFieldTypeRichtext,
+	}))
+
+	// Long multi-line HTML value, well over 255 chars, with quotes and commas
+	// to exercise CSV and JSON escaping
+	longHTML := "<p>This is a \"long\" description, with commas.</p>\n" +
+		"<pre><code>func main() {\n\tfmt.Println(\"hello\")\n}</code></pre>\n" +
+		"<p>" + strings.Repeat("Lorem ipsum dolor sit amet. ", 20) + "</p>"
+	require.Greater(t, len(longHTML), 255)
+
+	require.NoError(t, qasCSV.AddTestCase(TestCase{
+		Title:      "tc-with-richtext-description",
+		FolderPath: []string{"richtext"},
+		Priority:   "medium",
+		CustomFields: map[string]CustomFieldValue{
+			"description": {Value: longHTML},
+		},
+	}))
+
+	csvStr, err := qasCSV.GenerateCSV()
+	require.NoError(t, err)
+
+	// Parse the CSV back and verify the value round-trips
+	records, err := csv.NewReader(strings.NewReader(csvStr)).ReadAll()
+	require.NoError(t, err)
+	require.Len(t, records, 2)
+
+	header := records[0]
+	require.Equal(t, "custom_field_richtext_description", header[len(header)-1])
+
+	var cfValue CustomFieldValue
+	require.NoError(t, json.Unmarshal([]byte(records[1][len(header)-1]), &cfValue))
+	require.Equal(t, longHTML, cfValue.Value)
+}
+
+func TestLongTextCustomFieldValue(t *testing.T) {
+	qasCSV := NewQASphereCSV()
+	require.NoError(t, qasCSV.AddCustomField(CustomField{
+		SystemName: "notes",
+		Type:       CustomFieldTypeText,
+	}))
+
+	// Text custom field values have no length limit
+	err := qasCSV.AddTestCase(TestCase{
+		Title:      "tc-with-long-text-value",
+		FolderPath: []string{"root"},
+		Priority:   "low",
+		CustomFields: map[string]CustomFieldValue{
+			"notes": {Value: strings.Repeat("a", 600)},
+		},
+	})
+	require.NoError(t, err)
+}
+
 func TestFolderSlashEscaping(t *testing.T) {
 	qasCSV := NewQASphereCSV()
 
diff --git a/qascsv.go b/qascsv.go
index a4f5166..4b53781 100644
--- a/qascsv.go
+++ b/qascsv.go
@@ -11,6 +11,7 @@ import (
 	"os"
 	"strconv"
 	"strings"
+	"unicode/utf8"
 
 	"github.com/go-playground/validator/v10"
 	"github.com/hashicorp/go-multierror"
@@ -87,17 +88,31 @@ type ParameterValue struct {
 type CustomFieldType string
 
 const (
-	CustomFieldTypeText     CustomFieldType = "text"
+	// CustomFieldTypeText is a plain text field.
+	CustomFieldTypeText CustomFieldType = "text"
+	// CustomFieldTypeDropdown is a selection field. The value must match one
+	// of the options defined for the field in QA Sphere (option values are
+	// limited to 255 characters).
 	CustomFieldTypeDropdown CustomFieldType = "dropdown"
+	// CustomFieldTypeRichtext is a rich text field (e.g. the Description
+	// field). Unlike Preconditions and Steps, which take markdown, richtext
+	// values are HTML, e.g. "<p>…</p>" or "<pre><code>…</code></pre>".
+	// QA Sphere sanitizes the HTML on import using an allowlist of tags and
+	// attributes; disallowed markup is stripped.
+	CustomFieldTypeRichtext CustomFieldType = "richtext"
 )
 
 type CustomField struct {
 	SystemName string          `validate:"required,max=64"`
-	Type       CustomFieldType `validate:"required,oneof=text dropdown"`
+	Type       CustomFieldType `validate:"required,oneof=text dropdown richtext"`
 }
 
+// CustomFieldValue represents the value of a custom field on a test case.
+// QA Sphere does not limit the length of custom field values, but dropdown
+// values must match one of the field's options, which are limited to 255
+// characters.
 type CustomFieldValue struct {
-	Value     string `json:"value" validate:"max=255"`
+	Value     string `json:"value"`
 	IsDefault bool   `json:"isDefault" validate:"omitempty"`
 }
 
@@ -128,8 +143,9 @@ type TestCase struct {
 	// filter or organise related test cases and also helps in creating
 	// test runs. (optional)
 	Tags []string `validate:"dive,required,max=255"`
-	// The preconditions (or description) for the test case. Markdown is
-	// supported. (optional)
+	// The preconditions for the test case. Markdown is supported. (optional)
+	// For test case descriptions, use a richtext custom field instead —
+	// see CustomFieldTypeRichtext.
 	Preconditions string
 	// The sequence of (ordered) actions to be performed while executing
 	// the test case. (optional)
@@ -311,17 +327,22 @@ func (q *QASphereCSV) validateTestCase(tc TestCase) error {
 	}
 
 	if tc.CustomFields != nil {
-		for systemName := range tc.CustomFields {
-			var found bool
-			for _, cf := range q.customFields {
+		for systemName, cfValue := range tc.CustomFields {
+			var found *CustomField
+			for i, cf := range q.customFields {
 				if cf.SystemName == systemName {
-					found = true
+					found = &q.customFields[i]
 					break
 				}
 			}
-			if !found {
+			if found == nil {
 				return errors.Errorf("custom field %s is not defined in QASphereCSV.customFields", systemName)
 			}
+			// Dropdown values must match an option defined in QA Sphere,
+			// and options are limited to 255 characters.
+			if found.Type == CustomFieldTypeDropdown && utf8.RuneCountInString(cfValue.Value) > 255 {
+				return errors.Errorf("custom field %s: dropdown value must not exceed 255 characters", systemName)
+			}
 		}
 	}