Add :shadow-cljs-repl-message config flag to disable REPL mode status messages

Allows users to suppress the shadow-cljs mode status message prepended to
every eval result. When false, also skips the mode detection probe entirely.
Configurable via config.edn or CLI option. Defaults to true (existing behavior).

Closes #150

Author: Bruce Hauman

CONFIG.md

@@ -95,6 +95,19 @@ Boolean flag to control bash command execution mode (default: `true`). This sett
 - Both modes apply consistent output truncation (8500 chars total, split between stdout/stderr)
 - Local execution may be faster for simple commands but requires the MCP server to have necessary tools installed
 
+### `:shadow-cljs-repl-message`
+Controls whether the shadow-cljs REPL mode status message is included in eval results (default: `true`). When connected to a shadow-cljs nREPL server, a status message about the current CLJS mode is prepended to every eval result. This helps AI assistants understand the REPL state but can be disabled if you find it unnecessary.
+
+**Available values:**
+- `true` (default) - Includes the shadow-cljs mode status message in eval results
+- `false` - Disables the message and skips the mode detection probe entirely
+
+**When to use each setting:**
+- `true` - Best for most users, especially when the AI assistant needs to understand whether the REPL is in CLJS mode
+- `false` - When you manage REPL state yourself (e.g., via CLAUDE.md instructions) and want to reduce noise in eval output
+
+This can also be set via the CLI: `:shadow-cljs-repl-message false`
+
 ### `:dispatch-agent-context`
 Primes the dispatch agent with details about your code to help it find answers more quickly and accurately.
 

README.md

@@ -529,6 +529,11 @@ When used without `:port`, the MCP server will automatically parse the port from
 
 `:nrepl-env-type :bb`
 
+#### `:shadow-cljs-repl-message`
+**Optional** - Controls whether the shadow-cljs REPL mode status message is included in eval results (default: `true`). When connected to a shadow-cljs nREPL, a status message about CLJS mode is prepended to every eval result. Set to `false` to disable this message.
+
+`:shadow-cljs-repl-message false`
+
 #### `:config-profile`
 **Optional** - Load a built-in configuration profile that adjusts tool availability and descriptions. Useful for tailoring ClojureMCP to specific use cases.
 

src/clojure_mcp/config.clj

@@ -268,6 +268,15 @@
       false
       (boolean value))))
 
+(defn get-shadow-cljs-repl-message
+  "Returns whether the shadow-cljs REPL mode status message should be
+   included in eval results. Defaults to true."
+  [nrepl-client-map]
+  (let [value (get-config nrepl-client-map :shadow-cljs-repl-message)]
+    (if (nil? value)
+      true
+      (boolean value))))
+
 (defn clojure-env?
   "Returns true if the nREPL environment is a Clojure environment."
   [nrepl-client-map]

src/clojure_mcp/config/schema.clj

@@ -265,6 +265,7 @@
    [:bash-over-nrepl {:optional true} :boolean]
    [:nrepl-env-type {:optional true} [:enum :clj :bb :basilisp :scittle]]
    [:start-nrepl-cmd {:optional true} [:sequential NonBlankString]]
+   [:shadow-cljs-repl-message {:optional true} :boolean]
 
 ;; Scratch pad configuration
    [:scratch-pad-load {:optional true} :boolean]

src/clojure_mcp/core.clj

@@ -270,6 +270,24 @@
                                env-type))]
       (assoc nrepl-client-map ::config/config (assoc config :nrepl-env-type final-env-type)))))
 
+(def ^:private cli-config-override-keys
+  "Keys from the startup opts that override config.edn values."
+  [:shadow-cljs-repl-message])
+
+(defn- apply-cli-config-overrides
+  "Applies CLI option overrides to the config attached to an nrepl-client-map.
+   Only overrides keys that are explicitly provided (non-nil) in opts."
+  [nrepl-client-map opts]
+  (let [overrides (reduce (fn [m k]
+                            (if (some? (get opts k))
+                              (assoc m k (get opts k))
+                              m))
+                          {}
+                          cli-config-override-keys)]
+    (if (seq overrides)
+      (update nrepl-client-map ::config/config merge overrides)
+      nrepl-client-map)))
+
 (defn create-and-start-nrepl-connection
   "Creates an nREPL client map and loads configuration.
 
@@ -282,7 +300,7 @@
    when the first eval-code call is made.
 
    Takes initial-config map with optional :port, :host, :project-dir, :nrepl-env-type,
-   :config-file, :config-profile.
+   :config-file, :config-profile, :shadow-cljs-repl-message.
    - If :project-dir is provided, uses it directly (no REPL query needed)
    - If :project-dir is NOT provided, queries REPL for project directory (requires :port)
    - If :config-profile is provided, merges profile overlay on top of base config
@@ -293,24 +311,27 @@
     (log/info "Creating nREPL client for port" port)
     (log/info "Starting without nREPL connection (project-dir mode)"))
   (try
-    (let [nrepl-client-map (nrepl/create (dissoc initial-config :project-dir :nrepl-env-type :config-profile))
+    (let [nrepl-client-map (nrepl/create (apply dissoc initial-config
+                                                :project-dir :nrepl-env-type :config-profile
+                                                cli-config-override-keys))
           cli-env-type (:nrepl-env-type initial-config)
-          _ (log/info "nREPL client map created")]
-      (if project-dir
-        ;; Project dir provided - load config directly, no REPL query needed
-        (let [user-dir (.getCanonicalPath (io/file project-dir))
-              _ (log/info "Working directory set to:" user-dir)
-              config (load-config-handling-validation-errors config-file user-dir config-profile)
-              ;; Use cli-env-type or config's env-type, default to :clj
-              final-env-type (or cli-env-type
-                                 (:nrepl-env-type config)
-                                 :clj)]
-          (assoc nrepl-client-map ::config/config (assoc config :nrepl-env-type final-env-type)))
-        ;; No project dir - need to query REPL (requires port)
-        (let [;; Detect environment type (uses describe op, no full init needed)
-              env-type (nrepl/detect-nrepl-env-type nrepl-client-map)
-              _ (nrepl/set-port-env-type! nrepl-client-map env-type)]
-          (fetch-config nrepl-client-map config-file cli-env-type env-type project-dir config-profile))))
+          _ (log/info "nREPL client map created")
+          result (if project-dir
+                   ;; Project dir provided - load config directly, no REPL query needed
+                   (let [user-dir (.getCanonicalPath (io/file project-dir))
+                         _ (log/info "Working directory set to:" user-dir)
+                         config (load-config-handling-validation-errors config-file user-dir config-profile)
+                         ;; Use cli-env-type or config's env-type, default to :clj
+                         final-env-type (or cli-env-type
+                                            (:nrepl-env-type config)
+                                            :clj)]
+                     (assoc nrepl-client-map ::config/config (assoc config :nrepl-env-type final-env-type)))
+                   ;; No project dir - need to query REPL (requires port)
+                   (let [;; Detect environment type (uses describe op, no full init needed)
+                         env-type (nrepl/detect-nrepl-env-type nrepl-client-map)
+                         _ (nrepl/set-port-env-type! nrepl-client-map env-type)]
+                     (fetch-config nrepl-client-map config-file cli-env-type env-type project-dir config-profile)))]
+      (apply-cli-config-overrides result initial-config))
     (catch Exception e
       (log/error e "Failed to create nREPL connection")
       (throw e))))
@@ -369,9 +390,10 @@
                                   (catch Exception _ false))))
 (s/def ::start-nrepl-cmd (s/coll-of string? :kind vector?))
 (s/def ::config-profile (s/or :keyword keyword? :symbol symbol? :string string?))
+(s/def ::shadow-cljs-repl-message boolean?)
 (s/def ::nrepl-args (s/keys :req-un []
                             :opt-un [::port ::host ::config-file ::project-dir ::nrepl-env-type
-                                     ::start-nrepl-cmd ::config-profile]))
+                                     ::start-nrepl-cmd ::config-profile ::shadow-cljs-repl-message]))
 
 (def nrepl-client-atom (atom nil))
 

src/clojure_mcp/tools/eval/core.clj

@@ -65,8 +65,9 @@
 
    For shadow-cljs, prepends a mode status message."
   ([outputs] (partition-and-format-outputs outputs nil))
-  ([outputs {:keys [env-type shadow-cljs-mode?] :as _context}]
-   (let [prefix (when (= env-type :shadow)
+  ([outputs {:keys [env-type shadow-cljs-mode? show-shadow-message?]}]
+   (let [prefix (when (and (= env-type :shadow)
+                           (not (false? show-shadow-message?)))
                   [(shadow-cljs-mode-message shadow-cljs-mode?)])
          formatted (mapv #(format-eval-outputs % env-type) (partition-outputs outputs))]
      (if prefix

src/clojure_mcp/tools/eval/tool.clj

@@ -92,16 +92,18 @@ Examples:
     (try
       (let [client (nrepl/with-port-initialized base-client port)
             env-type (nrepl/get-port-env-type client)
-            ;; Check CLJS mode for shadow-cljs
-            cljs-mode? (when (= env-type :shadow)
+            show-shadow-msg? (config/get-shadow-cljs-repl-message base-client)
+            ;; Check CLJS mode for shadow-cljs (skip probe if message disabled)
+            cljs-mode? (when (and (= env-type :shadow) show-shadow-msg?)
                          (nrepl/shadow-cljs-mode? client session-type))
             ;; Execute the eval
             eval-result (core/evaluate-with-repair client (cond-> inputs
                                                             session-type (assoc :session-type session-type)
                                                             (nil? timeout_ms) (assoc :timeout_ms timeout)))]
         ;; Add context to result for formatting
         (assoc eval-result :context {:env-type env-type
-                                     :shadow-cljs-mode? cljs-mode?}))
+                                     :shadow-cljs-mode? cljs-mode?
+                                     :show-shadow-message? show-shadow-msg?}))
       (catch java.net.ConnectException e
         {:outputs [[:err (format "Failed to connect to nREPL server on port %d: %s. Ensure an nREPL server is running on that port."
                                  port (.getMessage e))]]