diff --git a/ROADMAP.md b/ROADMAP.md
index e21cdc79..b57f5782 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -7901,8 +7901,12 @@ Original filing (2026-04-18): the session emitted `SessionStart hook (completed)
 
     **Acceptance.** `claw --output-format json /commit` hint does NOT mention `--resume`. `claw --output-format json /status` (resume-safe) hint still mentions `--resume`. [SCOPE: claw-code]
 
-830. **`claw mcp show` (missing server name arg) emits `error_kind:"unknown_mcp_action"` instead of `missing_argument`** — dogfooded 2026-05-29 17:00 on `main` `ac5b19de`. `claw --output-format json mcp show` (no server name supplied) exits with `error_kind:"unknown_mcp_action"`. However `show` IS a known MCP action — the error is a missing required argument (server name), not an unknown action. Machine consumers inspecting `error_kind` cannot distinguish "I don't know this action" from "I know this action but a required arg is missing".
+830. **DONE — `claw mcp show` (missing server name arg) emits `error_kind:"unknown_mcp_action"` instead of `missing_argument`** — dogfooded 2026-05-29 17:00 on `main` `ac5b19de`. `claw --output-format json mcp show` (no server name supplied) exits with `error_kind:"unknown_mcp_action"`. However `show` IS a known MCP action — the error is a missing required argument (server name), not an unknown action. Machine consumers inspecting `error_kind` cannot distinguish "I don't know this action" from "I know this action but a required arg is missing".
 
     **Required fix shape.** The MCP subcommand parser should detect `show` with no following token and emit `missing_argument: mcp show requires a server name.\nUsage: claw mcp show <server>` with a distinct `error_kind`. Update the classifier arm to return `missing_argument` for this prefix.
 
     **Acceptance.** `claw --output-format json mcp show` exits rc=1, stdout `error_kind:"missing_argument"`, stderr empty. Hint contains usage example. [SCOPE: claw-code]
+
+    **Fix applied.** `mcp show` without a server name now emits a typed `missing_argument` response instead of reusing `unknown_mcp_action`. The direct JSON path returns `{kind:"mcp", action:"show", status:"error", error_kind:"missing_argument"}` with a usage hint on stdout and an empty stderr stream; the slash-command parser also classifies `/mcp show` as `missing_argument` via the shared error-kind classifier.
+
+    **Verification.** `cargo fmt --manifest-path rust/Cargo.toml --all -- --check`; `cargo test --manifest-path rust/Cargo.toml -p commands mcp -- --nocapture`; `cargo test --manifest-path rust/Cargo.toml -p rusty-claude-cli mcp_show_missing_server_name_returns_missing_argument_830 -- --nocapture`; `cargo test --manifest-path rust/Cargo.toml -p rusty-claude-cli classify_error_kind_returns_correct_discriminants -- --nocapture`; direct probe `cargo run --manifest-path rust/Cargo.toml -q -p rusty-claude-cli -- --output-format json mcp show`.
diff --git a/rust/crates/commands/src/lib.rs b/rust/crates/commands/src/lib.rs
index a8fd88d5..79d401be 100644
--- a/rust/crates/commands/src/lib.rs
+++ b/rust/crates/commands/src/lib.rs
@@ -1670,7 +1670,11 @@ fn parse_mcp_command(args: &[&str]) -> Result<SlashCommand, SlashCommandParseErr
             target: None,
         }),
         ["list", ..] => Err(usage_error("mcp list", "")),
-        ["show"] => Err(usage_error("mcp show", "<server>")),
+        ["show"] => Err(command_error(
+            "missing_argument: mcp show requires a server name.",
+            "mcp",
+            "/mcp show <server>",
+        )),
         ["show", target] => Ok(SlashCommand::Mcp {
             action: Some("show".to_string()),
             target: Some((*target).to_string()),
@@ -2918,12 +2922,12 @@ fn render_mcp_report_for(
             }
         }
         Some(args) if is_help_arg(args) => Ok(render_mcp_usage(None)),
-        Some("show") => Ok(render_mcp_usage(Some("show"))),
+        Some("show") => Ok(render_mcp_missing_argument_text("show")),
         Some(args) if args.split_whitespace().next() == Some("show") => {
             let mut parts = args.split_whitespace();
             let _ = parts.next();
             let Some(server_name) = parts.next() else {
-                return Ok(render_mcp_usage(Some("show")));
+                return Ok(render_mcp_missing_argument_text("show"));
             };
             if parts.next().is_some() {
                 return Ok(render_mcp_usage(Some(args)));
@@ -3027,12 +3031,12 @@ fn render_mcp_report_json_for(
             }
         }
         Some(args) if is_help_arg(args) => Ok(render_mcp_usage_json(None)),
-        Some("show") => Ok(render_mcp_usage_json(Some("show"))),
+        Some("show") => Ok(render_mcp_missing_argument_json("show")),
         Some(args) if args.split_whitespace().next() == Some("show") => {
             let mut parts = args.split_whitespace();
             let _ = parts.next();
             let Some(server_name) = parts.next() else {
-                return Ok(render_mcp_usage_json(Some("show")));
+                return Ok(render_mcp_missing_argument_json("show"));
             };
             if parts.next().is_some() {
                 return Ok(render_mcp_usage_json(Some(args)));
@@ -4269,6 +4273,44 @@ fn render_mcp_usage(unexpected: Option<&str>) -> String {
     lines.join("\n")
 }
 
+fn render_mcp_missing_argument_text(action: &str) -> String {
+    let hint = match action {
+        "show" => "use `claw mcp show <server>` to inspect a server",
+        _ => "provide the required argument for this MCP action",
+    };
+    format!(
+        "MCP\n  Error            missing argument for '{action}'\n  Hint             {hint}\n  Usage            /mcp [list|show <server>|help]"
+    )
+}
+
+fn render_mcp_missing_argument_json(action: &str) -> Value {
+    let (message, hint) = match action {
+        "show" => (
+            "mcp show requires a server name",
+            "Usage: claw mcp show <server>",
+        ),
+        _ => (
+            "mcp action requires an argument",
+            "Usage: claw mcp [list|show <server>|help]",
+        ),
+    };
+    json!({
+        "kind": "mcp",
+        "action": action,
+        "ok": false,
+        "status": "error",
+        "error_kind": "missing_argument",
+        "message": message,
+        "hint": hint,
+        "usage": {
+            "slash_command": "/mcp [list|show <server>|help]",
+            "direct_cli": "claw mcp [list|show <server>|help]",
+            "sources": [".claw/settings.json", ".claw/settings.local.json"],
+        },
+        "unexpected": Value::Null,
+    })
+}
+
 fn render_mcp_usage_json(unexpected: Option<&str>) -> Value {
     // #748: add error_kind when unexpected is set, matching agents/plugins unknown-subcommand shape.
     let error_kind: Value = if unexpected.is_some() {
diff --git a/rust/crates/rusty-claude-cli/src/main.rs b/rust/crates/rusty-claude-cli/src/main.rs
index 5febf841..554b47bb 100644
--- a/rust/crates/rusty-claude-cli/src/main.rs
+++ b/rust/crates/rusty-claude-cli/src/main.rs
@@ -297,6 +297,8 @@ fn classify_error_kind(message: &str) -> &'static str {
         "session_load_failed"
     } else if message.contains("unsupported ACP invocation") {
         "unsupported_acp_invocation"
+    } else if message.starts_with("missing_argument:") {
+        "missing_argument"
     } else if message.contains("unsupported skills action") {
         "unsupported_skills_action"
     } else if message.contains("unrecognized argument") || message.contains("unknown option") {
@@ -13476,6 +13478,11 @@ mod tests {
             classify_error_kind("unknown_option: unknown system-prompt option: --foo."),
             "unknown_option"
         );
+        // #830: known command with missing required argument must not collapse to unknown.
+        assert_eq!(
+            classify_error_kind("missing_argument: mcp show requires a server name."),
+            "missing_argument"
+        );
     }
 
     #[test]
diff --git a/rust/crates/rusty-claude-cli/tests/output_format_contract.rs b/rust/crates/rusty-claude-cli/tests/output_format_contract.rs
index 240884bf..7a2189cc 100644
--- a/rust/crates/rusty-claude-cli/tests/output_format_contract.rs
+++ b/rust/crates/rusty-claude-cli/tests/output_format_contract.rs
@@ -2448,6 +2448,38 @@ fn agents_plugins_mcp_unknown_subcommand_have_hint_774() {
     }
 }
 
+#[test]
+fn mcp_show_missing_server_name_returns_missing_argument_830() {
+    let root = unique_temp_dir("mcp-show-missing-830");
+    fs::create_dir_all(&root).expect("temp dir");
+
+    let output = run_claw(&root, &["--output-format", "json", "mcp", "show"], &[]);
+    assert!(
+        !output.status.success(),
+        "mcp show without server must fail"
+    );
+    assert_eq!(output.status.code(), Some(1), "exit code must be 1 (#830)");
+    assert!(
+        output.stderr.is_empty(),
+        "JSON mcp show missing-argument error must keep stderr empty (#830), got: {}",
+        String::from_utf8_lossy(&output.stderr)
+    );
+    let parsed: serde_json::Value = serde_json::from_slice(&output.stdout)
+        .expect("mcp show missing server should emit valid JSON on stdout");
+    assert_eq!(parsed["kind"], "mcp");
+    assert_eq!(parsed["action"], "show");
+    assert_eq!(parsed["status"], "error");
+    assert_eq!(parsed["error_kind"], "missing_argument");
+    assert!(
+        parsed["hint"]
+            .as_str()
+            .unwrap_or_default()
+            .contains("mcp show <server>"),
+        "hint should contain usage example, got: {}",
+        parsed["hint"]
+    );
+}
+
 #[test]
 fn interactive_only_guard_batch_769_to_771() {
     // #769-#771: a sweep of slash-only verbs with args that previously fell to