diff --git a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/ProbeCommand.cs b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/ProbeCommand.cs
index d2d46458..9c31bffe 100644
--- a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/ProbeCommand.cs
+++ b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/ProbeCommand.cs
@@ -28,6 +28,7 @@ public sealed class ProbeCommand : FocasCommandBase
     {
         ConfigureLogging();
         ValidateOptions();
+        ValidateDataType(Address, DataType);
         var ct = console.RegisterCancellationHandler();
 
         var probeTag = new FocasTagDefinition(
diff --git a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/ReadCommand.cs b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/ReadCommand.cs
index df042344..9218a2c9 100644
--- a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/ReadCommand.cs
+++ b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/ReadCommand.cs
@@ -19,7 +19,7 @@ public sealed class ReadCommand : FocasCommandBase
 
     /// <summary>Gets the data type to interpret the address as.</summary>
     [CommandOption("type", 't', Description =
-        "Bit / Byte / Int16 / Int32 / Float32 / Float64 / String (default Int16).")]
+        "Bit / Byte / Int16 / Int32 / Float32 / Float64 / String (default Int16). String only on FIXED: paths.")]
     public FocasDataType DataType { get; init; } = FocasDataType.Int16;
 
     /// <inheritdoc />
@@ -28,6 +28,7 @@ public sealed class ReadCommand : FocasCommandBase
         ConfigureLogging();
         // Validate numeric option ranges before any driver work.
         ValidateOptions();
+        ValidateDataType(Address, DataType);
         var ct = console.RegisterCancellationHandler();
 
         var tagName = SynthesiseTagName(Address, DataType);
diff --git a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/SubscribeCommand.cs b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/SubscribeCommand.cs
index 1a3cb5f4..ee126fc0 100644
--- a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/SubscribeCommand.cs
+++ b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/SubscribeCommand.cs
@@ -18,7 +18,7 @@ public sealed class SubscribeCommand : FocasCommandBase
 
     /// <summary>Gets the data type of the address.</summary>
     [CommandOption("type", 't', Description =
-        "Bit / Byte / Int16 / Int32 / Float32 / Float64 / String (default Int16).")]
+        "Bit / Byte / Int16 / Int32 / Float32 / Float64 / String (default Int16). String only on FIXED: paths.")]
     public FocasDataType DataType { get; init; } = FocasDataType.Int16;
 
     /// <summary>Gets the polling interval in milliseconds.</summary>
@@ -33,6 +33,7 @@ public sealed class SubscribeCommand : FocasCommandBase
         // --interval-ms) before any driver work so a zero/negative interval surfaces as a
         // clean CommandException rather than a tight-spinning poll loop.
         ValidateOptions(IntervalMs);
+        ValidateDataType(Address, DataType);
         var ct = console.RegisterCancellationHandler();
 
         var tagName = ReadCommand.SynthesiseTagName(Address, DataType);
diff --git a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/WriteCommand.cs b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/WriteCommand.cs
index bd383041..22cfb431 100644
--- a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/WriteCommand.cs
+++ b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/Commands/WriteCommand.cs
@@ -20,7 +20,7 @@ public sealed class WriteCommand : FocasCommandBase
 
     /// <summary>Gets the data type of the value to write.</summary>
     [CommandOption("type", 't', Description =
-        "Bit / Byte / Int16 / Int32 / Float32 / Float64 / String (default Int16).")]
+        "Bit / Byte / Int16 / Int32 / Float32 / Float64 / String (default Int16). String only on FIXED: paths.")]
     public FocasDataType DataType { get; init; } = FocasDataType.Int16;
 
     /// <summary>Gets the value to write.</summary>
@@ -37,6 +37,7 @@ public sealed class WriteCommand : FocasCommandBase
         // port/timeout surfaces as a clean CommandException rather than an opaque
         // downstream exception.
         ValidateOptions();
+        ValidateDataType(Address, DataType);
         var ct = console.RegisterCancellationHandler();
 
         var tagName = ReadCommand.SynthesiseTagName(Address, DataType);
diff --git a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/FocasCommandBase.cs b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/FocasCommandBase.cs
index 62965d52..e57ce8bf 100644
--- a/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/FocasCommandBase.cs
+++ b/src/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli/FocasCommandBase.cs
@@ -89,4 +89,17 @@ public abstract class FocasCommandBase : DriverCommandBase
             throw new CliFx.Exceptions.CommandException(
                 $"--interval-ms must be positive (got {iv}).");
     }
+
+    /// <summary>
+    ///     Refuses an <c>--address</c> / <c>--type</c> pair the driver cannot serve (String on a PMC / PARAM / MACRO
+    ///     address — the driver skips such a tag, so the command would only ever print BadNodeIdUnknown). Same
+    ///     rule as the driver and the AdminUI editor: <see cref="FocasTagDefinitionFactory.DescribeDataTypeMismatch"/>.
+    /// </summary>
+    /// <param name="address">The FOCAS address.</param>
+    /// <param name="type">The data type.</param>
+    protected static void ValidateDataType(string address, FocasDataType type)
+    {
+        if (FocasTagDefinitionFactory.DescribeDataTypeMismatch(type, address) is { } error)
+            throw new CliFx.Exceptions.CommandException(error);
+    }
 }
diff --git a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasTagDefinitionFactory.cs b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasTagDefinitionFactory.cs
index d495dad1..b65150f6 100644
--- a/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasTagDefinitionFactory.cs
+++ b/src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Contracts/FocasTagDefinitionFactory.cs
@@ -53,6 +53,9 @@ public static class FocasTagDefinitionFactory
             // Strict enum read: a typo'd dataType rejects the tag (→ BadNodeIdUnknown)
             // instead of silently defaulting to a wrong-width Good.
             if (!TagConfigJson.TryReadEnumStrict(root, "dataType", FocasDataType.Int32, out var dataType)) return false;
+            // A data type no read of this address can produce (String on PMC / PARAM / MACRO) rejects the tag:
+            // served, it published a boxed number at Good into a String node.
+            if (DescribeDataTypeMismatch(dataType, address) is not null) return false;
             // FOCAS authored tags carry no `writable` key (writability lives on the Tag entity / node ACL):
             // absent ⇒ read-only. An explicit writable:true is honoured for the driver's internal write gate
             // (default-false, so a missing key stays read-only — the note is preserved).
@@ -73,6 +76,26 @@ public static class FocasTagDefinitionFactory
         catch (InvalidOperationException) { return false; }
     }
 
+    /// <summary>
+    ///     The ONE address/data-type compatibility rule, shared by the mapper (and so the driver's init and the
+    ///     deploy inspector), the AdminUI tag editor and the CLI. <see cref="FocasDataType.String"/> is only
+    ///     servable from the fixed tree (Identity / Program name / mode text …): a PMC, parameter or macro read
+    ///     returns a number, which a String node would receive at Good. An <c>ALARM:</c> tag has no value, so its
+    ///     data type is irrelevant; an unparseable address is left to the address check, which names it better.
+    /// </summary>
+    /// <param name="dataType">The authored data type.</param>
+    /// <param name="address">The authored address.</param>
+    /// <returns>The reason the pair cannot be served, or <see langword="null"/> when it can.</returns>
+    public static string? DescribeDataTypeMismatch(FocasDataType dataType, string? address)
+    {
+        if (dataType != FocasDataType.String) return null;
+        var parsed = FocasAddress.TryParse(address);
+        if (parsed is null || parsed.Kind is FocasAreaKind.Fixed or FocasAreaKind.Alarm) return null;
+        return $"FOCAS data type 'String' is not readable at '{address!.Trim()}' — PMC, PARAM: and MACRO: reads " +
+               "return numbers (String is only valid on FIXED: paths such as FIXED:Identity/SeriesNumber). " +
+               "Choose Bit / Byte / Int16 / Int32 / Float32 / Float64.";
+    }
+
     /// <summary>
     ///     The tag's cross-driver <c>alarm</c> object, or <see langword="null"/> when it carries none.
     ///     Lenient like the host's <c>TagConfigIntent</c>: a non-integer <c>severity</c> is simply absent.
@@ -236,6 +259,10 @@ public static class FocasTagDefinitionFactory
         }
 
         if (TagConfigJson.DescribeInvalidEnum<FocasDataType>(root, "dataType") is { } w) rejections.Add(w);
+        else if (addr.ValueKind == JsonValueKind.String
+                 && TagConfigJson.TryReadEnumStrict(root, "dataType", FocasDataType.Int32, out var dataType)
+                 && DescribeDataTypeMismatch(dataType, addr.GetString()) is { } mismatch)
+            rejections.Add(mismatch + " The driver will skip this tag and it will read BadNodeIdUnknown.");
     }
 
     /// <summary>
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/FocasTagConfigEditor.razor b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/FocasTagConfigEditor.razor
index 8911b438..03fd6a15 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/FocasTagConfigEditor.razor
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagEditors/FocasTagConfigEditor.razor
@@ -15,8 +15,22 @@
     </div>
     <div class="col-md-3"><label class="form-label">Data type</label>
         <select class="form-select form-select-sm" value="@_m.DataType" @onchange="@(e => Update(() => _m.DataType = ParseEnum(e.Value, FocasDataType.Int32)))">
-            @foreach (var v in Enum.GetValues<FocasDataType>()) { <option value="@v">@v</option> }
-        </select></div>
+            @foreach (var v in Enum.GetValues<FocasDataType>())
+            {
+                @* String is only readable from the fixed tree (FocasTagDefinitionFactory.DescribeDataTypeMismatch):
+                   offered there, and kept visible when a loaded blob already carries it so the select never lies. *@
+                if (v != FocasDataType.String || _m.DataType == FocasDataType.String
+                    || FocasTagDefinitionFactory.DescribeDataTypeMismatch(v, _m.Address) is null)
+                {
+                    <option value="@v">@v</option>
+                }
+            }
+        </select>
+        @if (FocasTagDefinitionFactory.DescribeDataTypeMismatch(_m.DataType, _m.Address) is { } typeError)
+        {
+            <div class="form-text text-danger small">@typeError</div>
+        }
+    </div>
     <div class="col-12">
         <div class="form-check">
             <input type="checkbox" class="form-check-input" id="focas-writable" disabled checked="false" />
diff --git a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/FocasTagConfigModel.cs b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/FocasTagConfigModel.cs
index 91851b8e..68904dff 100644
--- a/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/FocasTagConfigModel.cs
+++ b/src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Uns/TagEditors/FocasTagConfigModel.cs
@@ -80,6 +80,10 @@ public sealed class FocasTagConfigModel
         // ahead of the parse consult below and is never replaced by it.
         if (FocasAddress.TryParse(Address) is null) return DescribeUnparseableAddress(Address);
 
+        // The driver's own address/data-type rule (String only on FIXED: paths) — checked on the typed fields so a
+        // model built in the editor is judged too, not only a loaded blob the parse gate below can see.
+        if (FocasTagDefinitionFactory.DescribeDataTypeMismatch(DataType, Address) is { } typeError) return typeError;
+
         // Parse-gate backstop. ⚠️ It gates on the PARSE VERDICT, never on Inspect being non-empty: FOCAS's
         // inspector emits advisories for blobs the reader ACCEPTS (an unparseable address, an authored
         // 'writable':true on a read-only wire), and promoting those to authoring errors would make the modal
diff --git a/tests/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli.Tests/FocasCommandBaseValidationTests.cs b/tests/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli.Tests/FocasCommandBaseValidationTests.cs
index 2efff255..66dcabde 100644
--- a/tests/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli.Tests/FocasCommandBaseValidationTests.cs
+++ b/tests/Drivers/Cli/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Cli.Tests/FocasCommandBaseValidationTests.cs
@@ -33,6 +33,27 @@ public sealed class FocasCommandBaseValidationTests
 
         /// <summary>Invokes option validation without interval.</summary>
         public void InvokeValidateNoInterval() => ValidateOptions(intervalMs: null);
+
+        /// <summary>Invokes the address/data-type check.</summary>
+        public void InvokeValidateDataType(string address, FocasDataType type) => ValidateDataType(address, type);
+    }
+
+    /// <summary>
+    ///     #740 / R07:U8 — <c>--type String</c> on a PMC / PARAM / MACRO address is refused at the CLI boundary
+    ///     (the driver would skip the tag and the read would print BadNodeIdUnknown); a fixed-tree path keeps it.
+    /// </summary>
+    [Theory]
+    [InlineData("R100", FocasDataType.String, false)]
+    [InlineData("MACRO:500", FocasDataType.String, false)]
+    [InlineData("PARAM:6711", FocasDataType.String, false)]
+    [InlineData("R100", FocasDataType.Byte, true)]
+    [InlineData("FIXED:Identity/SeriesNumber", FocasDataType.String, true)]
+    public void Validate_data_type_against_address(string address, FocasDataType type, bool ok)
+    {
+        var sut = new Probe { CncHost = "host", IntervalMs = 1000 };
+        if (ok) Should.NotThrow(() => sut.InvokeValidateDataType(address, type));
+        else Should.Throw<CliFx.Exceptions.CommandException>(() => sut.InvokeValidateDataType(address, type))
+            .Message.ShouldContain("String");
     }
 
     /// <summary>Verifies that default options are accepted.</summary>
diff --git a/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasStringDataTypeTests.cs b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasStringDataTypeTests.cs
new file mode 100644
index 00000000..600a205a
--- /dev/null
+++ b/tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests/FocasStringDataTypeTests.cs
@@ -0,0 +1,104 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+using ZB.MOM.WW.OtOpcUa.Driver.FOCAS;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.FOCAS.Tests;
+
+/// <summary>
+///     #740 / R07:U8 — <see cref="FocasDataType.String"/> was authorable on any address, but no area read
+///     produces a string: PMC fell through to a byte read, PARAM to an Int32, MACRO to a double, and a
+///     String-typed node received a boxed number at Good. String is now refused on PMC / PARAM / MACRO by the
+///     one shared check, everywhere a tag is authored or loaded; the fixed tree (Identity / Program name, …),
+///     whose values really are strings, keeps it.
+/// </summary>
+[Trait("Category", "Unit")]
+public sealed class FocasStringDataTypeTests
+{
+    private const string Host = "focas://10.0.0.5:8193";
+
+    private static string Config(string address, string dataType) =>
+        $$"""{"address":"{{address}}","dataType":"{{dataType}}"}""";
+
+    /// <summary>String on an area read is refused by the mapper.</summary>
+    [Theory]
+    [InlineData("R100")]
+    [InlineData("X0.0")]
+    [InlineData("PARAM:6711")]
+    [InlineData("MACRO:500")]
+    public void Mapper_refuses_string_on_an_area_read(string address)
+    {
+        FocasTagDefinitionFactory.FromTagConfig(Config(address, "String"), "raw/T", out _).ShouldBeFalse();
+        FocasTagDefinitionFactory.DescribeDataTypeMismatch(FocasDataType.String, address).ShouldNotBeNull();
+    }
+
+    /// <summary>Positive control: numeric types on the same addresses, and String on the fixed tree, still map.</summary>
+    [Theory]
+    [InlineData("R100", "Byte")]
+    [InlineData("PARAM:6711", "Int32")]
+    [InlineData("MACRO:500", "Float64")]
+    [InlineData("FIXED:Identity/SeriesNumber", "String")]
+    [InlineData("FIXED:Program/Name", "String")]
+    public void Mapper_accepts_numeric_area_reads_and_string_fixed_tree_paths(string address, string dataType)
+    {
+        FocasTagDefinitionFactory.FromTagConfig(Config(address, dataType), "raw/T", out var def).ShouldBeTrue();
+        def.Address.ShouldBe(address);
+    }
+
+    /// <summary>An ALARM: tag has no value, so its data type is irrelevant and String is not refused.</summary>
+    [Fact]
+    public void Mapper_accepts_string_on_an_alarm_tag()
+    {
+        FocasTagDefinitionFactory.FromTagConfig(
+            """{"address":"ALARM:*","dataType":"String","alarm":{"severity":500}}""", "raw/A", out _).ShouldBeTrue();
+    }
+
+    /// <summary>An unparseable address is left to the address check — it still draws THAT diagnosis.</summary>
+    [Fact]
+    public void Unparseable_address_keeps_its_own_diagnosis()
+    {
+        FocasTagDefinitionFactory.DescribeDataTypeMismatch(FocasDataType.String, "not-an-address").ShouldBeNull();
+        FocasTagDefinitionFactory.FromTagConfig(Config("not-an-address", "String"), "raw/T", out _).ShouldBeTrue();
+    }
+
+    /// <summary>The deploy-time inspector names the reason rather than falling to the generic backstop.</summary>
+    [Fact]
+    public void Inspect_names_the_string_refusal()
+    {
+        var warnings = FocasTagDefinitionFactory.Inspect(Config("MACRO:500", "String"));
+        warnings.ShouldContain(w => w.Contains("String", StringComparison.Ordinal) && w.Contains("MACRO:500", StringComparison.Ordinal));
+        FocasTagDefinitionFactory.Inspect(Config("MACRO:500", "Float64")).ShouldBeEmpty();
+    }
+
+    /// <summary>
+    ///     At init a String area tag is skipped and reported (never served as a Good number); the numeric tag
+    ///     beside it reads normally (positive control).
+    /// </summary>
+    [Fact]
+    public async Task Driver_skips_and_reports_a_string_area_tag()
+    {
+        var factory = new FakeFocasClientFactory
+        {
+            Customise = () => new FakeFocasClient { Values = { ["R100"] = (sbyte)7 } },
+        };
+        var drv = new FocasDriver(new FocasDriverOptions
+        {
+            Devices = [new FocasDeviceOptions(Host)],
+            RawTags =
+            [
+                new RawTagEntry("raw/Str", Config("R100", "String"), false, Host),
+                new RawTagEntry("raw/Num", Config("R100", "Byte"), false, Host),
+            ],
+            Probe = new FocasProbeOptions { Enabled = false },
+        }, "focas-u8", factory);
+        await drv.InitializeAsync("{}", CancellationToken.None);
+
+        var snaps = await drv.ReadAsync(["raw/Str", "raw/Num"], CancellationToken.None);
+        snaps[0].StatusCode.ShouldBe(FocasStatusMapper.BadNodeIdUnknown);
+        snaps[0].Value.ShouldBeNull();
+        snaps[1].StatusCode.ShouldBe(FocasStatusMapper.Good);
+        snaps[1].Value.ShouldBe((sbyte)7);
+        drv.GetSkippedTags()!.Sample.ShouldContain(s => s.RawPath == "raw/Str");
+        await drv.ShutdownAsync(CancellationToken.None);
+    }
+}
diff --git a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs
index 334637cd..b3f16e8b 100644
--- a/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs
+++ b/tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/FocasTagConfigModelTests.cs
@@ -169,4 +169,26 @@ public sealed class FocasTagConfigModelTests
     [InlineData("""{"address":"R100","dataType":2}""")]
     public void Validate_accepts_every_dataType_the_driver_accepts(string json)
         => FocasTagConfigModel.FromJson(json).Validate().ShouldBeNull();
+
+    /// <summary>
+    ///     #740 / R07:U8 — String on a PMC / PARAM / MACRO address is refused by the driver (no area read
+    ///     returns text), so the modal refuses it too, for a model built in the editor and for a loaded blob.
+    /// </summary>
+    [Theory]
+    [InlineData("R100")]
+    [InlineData("PARAM:6711")]
+    [InlineData("MACRO:500")]
+    public void Validate_refuses_string_on_an_area_address(string address)
+    {
+        new FocasTagConfigModel { Address = address, DataType = FocasDataType.String }
+            .Validate().ShouldNotBeNull().ShouldContain("String");
+        FocasTagConfigModel.FromJson($$"""{"address":"{{address}}","dataType":"String"}""")
+            .Validate().ShouldNotBeNull().ShouldContain("String");
+    }
+
+    /// <summary>Positive control: the fixed tree's string fields keep String.</summary>
+    [Fact]
+    public void Validate_accepts_string_on_a_fixed_tree_path()
+        => new FocasTagConfigModel { Address = "FIXED:Identity/SeriesNumber", DataType = FocasDataType.String }
+            .Validate().ShouldBeNull();
 }