A custom Swashbuckle schema filter that adds remarks to schema descriptions.

CustomXmlCommentsSchemaFilter.cs

using System.Xml.XPath;
using Microsoft.OpenApi.Models;

namespace Swashbuckle.AspNetCore.SwaggerGen;

// This is a slightly modified version of the built-in XmlCommentsSchemaFilter.
// Currently our only modifications are that we append the contents of the <remarks> section to the description for each schema item.

public class CustomXmlCommentsSchemaFilter : ISchemaFilter
{
    private readonly XPathNavigator _xmlNavigator;

    public CustomXmlCommentsSchemaFilter(XPathDocument xmlDoc)
    {
        _xmlNavigator = xmlDoc.CreateNavigator();
    }

    public void Apply(OpenApiSchema schema, SchemaFilterContext context)
    {
        ApplyTypeTags(schema, context.Type);

        if (context.MemberInfo != null)
        {
            ApplyMemberTags(schema, context);
        }
    }

    private void ApplyTypeTags(OpenApiSchema schema, Type type)
    {
        var typeMemberName = XmlCommentsNodeNameHelper.GetMemberNameForType(type);
        var typeNode = _xmlNavigator.SelectSingleNode($"/doc/members/member[@name='{typeMemberName}']");
        if (typeNode == null)
            return;

        var typeSummaryNode = typeNode.SelectSingleNode("summary");
        if (typeSummaryNode != null)
            schema.Description = XmlCommentsTextHelper.Humanize(typeSummaryNode.InnerXml);

        // This is the part we've added. Remarks are appended to the description with a couple of linebreaks in between.
        var typeRemarksNode = typeNode.SelectSingleNode("remarks");
        if (typeRemarksNode != null)
            schema.Description = $"{schema.Description}\r\n\r\n{XmlCommentsTextHelper.Humanize(typeRemarksNode.InnerXml)}";
    }

    private void ApplyMemberTags(OpenApiSchema schema, SchemaFilterContext context)
    {
        var fieldOrPropertyMemberName = XmlCommentsNodeNameHelper.GetMemberNameForFieldOrProperty(context.MemberInfo);
        var fieldOrPropertyNode = _xmlNavigator.SelectSingleNode($"/doc/members/member[@name='{fieldOrPropertyMemberName}']");

        if (fieldOrPropertyNode == null) return;

        var summaryNode = fieldOrPropertyNode.SelectSingleNode("summary");
        if (summaryNode != null)
            schema.Description = XmlCommentsTextHelper.Humanize(summaryNode.InnerXml);

        // This is the part we've added. Remarks are appended to the description with a couple of linebreaks in between.
        var remarksNode = fieldOrPropertyNode.SelectSingleNode("remarks");
        if (remarksNode != null)
            schema.Description = $"{schema.Description}\r\n\r\n{XmlCommentsTextHelper.Humanize(remarksNode.InnerXml)}";

        var exampleNode = fieldOrPropertyNode.SelectSingleNode("example");
        if (exampleNode != null)
        {
            var exampleAsJson = (schema.ResolveType(context.SchemaRepository) == "string")
                ? $"\"{exampleNode.InnerXml}\""
                : exampleNode.InnerXml;

            schema.Example = OpenApiAnyFactory.CreateFromJson(exampleAsJson);
        }
    }
}