diff --git a/schemas/profile.schema.json b/schemas/profile.schema.json
index 8d04739..aa67992 100644
--- a/schemas/profile.schema.json
+++ b/schemas/profile.schema.json
@@ -196,6 +196,34 @@
           "description": "Which vendor adapter files to generate"
         }
       }
+    },
+    "mcp": {
+      "type": "object",
+      "description": "Optional MCP server declarations. Written to all present vendor MCP config files on compose/sync.",
+      "additionalProperties": false,
+      "properties": {
+        "strategy": {
+          "type": "string",
+          "enum": ["merge", "replace"],
+          "default": "merge",
+          "description": "merge: profile servers are added without removing existing ones. replace: all vendor MCP files are fully replaced by the profile declaration."
+        },
+        "servers": {
+          "type": "object",
+          "description": "MCP server entries. Keys are server names; values follow the .mcp.json entry shape.",
+          "additionalProperties": {
+            "type": "object",
+            "required": ["type"],
+            "properties": {
+              "type":    { "type": "string", "enum": ["stdio", "http"] },
+              "command": { "type": "string" },
+              "args":    { "type": "array", "items": { "type": "string" } },
+              "url":     { "type": "string" },
+              "env":     { "type": "object", "additionalProperties": { "type": "string" } }
+            }
+          }
+        }
+      }
     }
   }
 }
diff --git a/tooling/lib/compose.sh b/tooling/lib/compose.sh
index ef62aca..f26d2f7 100755
--- a/tooling/lib/compose.sh
+++ b/tooling/lib/compose.sh
@@ -411,6 +411,19 @@ LOCK
       cp "$PROFILE_FILE" "$profile_dst"
     fi
 
+    # Seed MCP servers from profile (no-op if mcp key absent)
+    local has_mcp
+    has_mcp=$(yq '.mcp.servers // "null"' "$PROFILE_FILE")
+    if [[ "$has_mcp" != "null" && "$has_mcp" != "{}" ]]; then
+      local mcp_strategy
+      mcp_strategy=$(yq '.mcp.strategy // "merge"' "$PROFILE_FILE")
+      bash "$LIBRARY/tooling/lib/mcp.sh" \
+        --action seed \
+        --target "$TARGET" \
+        --profile-file "$PROFILE_FILE" \
+        --strategy "$mcp_strategy"
+    fi
+
     update_gitignore
     echo "Composed AGENTS.md → $TARGET/AGENTS.md"
   fi
@@ -619,6 +632,19 @@ compose_nested() {
     cp "$PROFILE_FILE" "$profile_dst"
   fi
 
+  # Seed MCP servers from profile (no-op if mcp key absent)
+  local has_mcp
+  has_mcp=$(yq '.mcp.servers // "null"' "$PROFILE_FILE")
+  if [[ "$has_mcp" != "null" && "$has_mcp" != "{}" ]]; then
+    local mcp_strategy
+    mcp_strategy=$(yq '.mcp.strategy // "merge"' "$PROFILE_FILE")
+    bash "$LIBRARY/tooling/lib/mcp.sh" \
+      --action seed \
+      --target "$TARGET" \
+      --profile-file "$PROFILE_FILE" \
+      --strategy "$mcp_strategy"
+  fi
+
   update_gitignore
   echo "Composed AGENTS.md → $TARGET/AGENTS.md"
 }
diff --git a/tooling/lib/mcp.sh b/tooling/lib/mcp.sh
index 2d2ddba..49727a9 100755
--- a/tooling/lib/mcp.sh
+++ b/tooling/lib/mcp.sh
@@ -6,12 +6,16 @@ set -euo pipefail
 ACTION=""
 TARGET=""
 NAME=""
+PROFILE_FILE=""
+STRATEGY="merge"
 
 while [[ $# -gt 0 ]]; do
   case "$1" in
     --action) ACTION="$2"; shift 2 ;;
     --target) TARGET="$2"; shift 2 ;;
     --name)   NAME="$2";   shift 2 ;;
+    --profile-file) PROFILE_FILE="$2"; shift 2 ;;
+    --strategy)     STRATEGY="$2";   shift 2 ;;
     *) echo "Unknown argument: $1" >&2; exit 1 ;;
   esac
 done
@@ -30,6 +34,10 @@ write_json() {
   local file="$1"
   local content="$2"
   local tmp
+  # Ensure parent directory exists
+  local dir
+  dir=$(dirname "$file")
+  mkdir -p "$dir"
   tmp=$(mktemp)
   printf '%s\n' "$content" > "$tmp"
   mv "$tmp" "$file"
@@ -285,10 +293,209 @@ action_remove() {
   echo "Done."
 }
 
+# ── Action: seed ─────────────────────────────────────────────────────────────────
+action_seed() {
+  local profile_file="$1"
+  local strategy="${2:-merge}"
+
+  # Get server names as array first
+  local server_names=()
+  while IFS= read -r name; do
+    [[ -n "$name" && "$name" != "null" ]] && server_names+=("$name")
+  done < <(yq '.mcp.servers | keys | .[]' "$profile_file" 2>/dev/null || true)
+
+  if [[ ${#server_names[@]} -eq 0 ]]; then
+    echo "No MCP servers declared in profile — skipping seed"
+    return 0
+  fi
+
+  # ── Seed .mcp.json (Claude) ──────────────────────────────────────────
+  local mcp_file="$TARGET/.mcp.json"
+  # Create or update .mcp.json if: file exists OR strategy is replace OR mcp.servers declared in profile
+  if [[ -f "$mcp_file" || "$strategy" == "replace" || "${#server_names[@]}" -gt 0 ]]; then
+    local existing_servers updated_servers
+    existing_servers="{}"
+    if [[ -f "$mcp_file" ]]; then
+      existing_servers=$(jq '.mcpServers // {}' "$mcp_file" 2>/dev/null || echo "{}")
+    fi
+
+    if [[ "$strategy" == "replace" ]]; then
+      # Build fresh JSON from profile - start with empty
+      updated_servers="{}"
+      local name
+      for name in "${server_names[@]}"; do
+        local server_yaml server_json
+        server_yaml=$(yq -r ".mcp.servers.$name" "$profile_file" 2>/dev/null || echo "")
+        if [[ -n "$server_yaml" && "$server_yaml" != "null" ]]; then
+          # Convert YAML to JSON using yq -o json
+          server_json=$(echo "$server_yaml" | yq -o json '.' 2>/dev/null || echo "{}")
+          updated_servers=$(printf '%s' "$updated_servers" | jq --arg n "$name" --argjson s "$server_json" '. + {($n): $s}')
+        fi
+      done
+    else
+      # Merge: add only if key doesn't exist
+      local name
+      for name in "${server_names[@]}"; do
+        local exists
+        exists=$(jq -r --arg n "$name" 'has($n)' "$existing_servers" 2>/dev/null || echo "false")
+        if [[ "$exists" == "false" ]]; then
+          local server_yaml server_json
+          server_yaml=$(yq -r ".mcp.servers.$name" "$profile_file" 2>/dev/null || echo "")
+          if [[ -n "$server_yaml" && "$server_yaml" != "null" ]]; then
+            # Convert YAML to JSON using yq -o json
+            server_json=$(echo "$server_yaml" | yq -o json '.' 2>/dev/null || echo "{}")
+            existing_servers=$(printf '%s' "$existing_servers" | jq --arg n "$name" --argjson s "$server_json" '. + {($n): $s}')
+          fi
+        fi
+      done
+      updated_servers="$existing_servers"
+    fi
+
+    local final_json
+    final_json=$(printf '{"mcpServers": %s}' "$updated_servers")
+    write_json "$mcp_file" "$final_json"
+    echo "  ✔  Seeded ${#server_names[@]} server(s) to .mcp.json (strategy: $strategy)"
+  fi
+
+  # ── Helper: translate a profile server entry to Opencode format ─────────
+  # Opencode differences from Claude/profile format:
+  #   - type: stdio→local, http→remote
+  #   - command+args → combined array under "command"
+  #   - env → environment
+  translate_to_opencode() {
+    local server_json="$1"
+    jq '
+      if .type == "stdio" then .type = "local"
+      elif .type == "http" then .type = "remote"
+      else . end
+      |
+      if .command != null then
+        . + { "command": ([ .command ] + (if .args != null then .args else [] end)) }
+        | del(.args)
+      else . end
+      |
+      if .env != null then
+        . + { "environment": .env } | del(.env)
+      else . end
+    ' <<< "$server_json"
+  }
+
+  # ── Helper: translate a profile server entry to Gemini format ────────────
+  # Gemini differences from Claude/profile format:
+  #   - No "type" field (transport inferred from field presence)
+  #   - url → httpUrl for http entries
+  translate_to_gemini() {
+    local server_json="$1"
+    jq '
+      if .type == "http" and .url != null then
+        . + { "httpUrl": .url } | del(.url)
+      else . end
+      |
+      del(.type)
+    ' <<< "$server_json"
+  }
+
+  # ── Seed opencode.json (Opencode) ────────────────────────────────────────
+  local opencode_file="$TARGET/opencode.json"
+  if [[ -f "$opencode_file" ]]; then
+    local existing_oc updated_oc
+    existing_oc=$(jq '.mcp // {}' "$opencode_file" 2>/dev/null || echo "{}")
+
+    if [[ "$strategy" == "replace" ]]; then
+      updated_oc="{}"
+      local name
+      for name in "${server_names[@]}"; do
+        local server_json oc_entry
+        server_json=$(yq -o json ".mcp.servers.$name" "$profile_file" 2>/dev/null || echo "{}")
+        if [[ -n "$server_json" && "$server_json" != "null" ]]; then
+          oc_entry=$(translate_to_opencode "$server_json")
+          updated_oc=$(printf '%s' "$updated_oc" | jq --arg n "$name" --argjson s "$oc_entry" '. + {($n): $s}')
+        fi
+      done
+    else
+      # Merge: add only if key doesn't already exist
+      local name
+      for name in "${server_names[@]}"; do
+        local exists
+        exists=$(printf '%s' "$existing_oc" | jq -r --arg n "$name" 'has($n)')
+        if [[ "$exists" == "false" ]]; then
+          local server_json oc_entry
+          server_json=$(yq -o json ".mcp.servers.$name" "$profile_file" 2>/dev/null || echo "{}")
+          if [[ -n "$server_json" && "$server_json" != "null" ]]; then
+            oc_entry=$(translate_to_opencode "$server_json")
+            existing_oc=$(printf '%s' "$existing_oc" | jq --arg n "$name" --argjson s "$oc_entry" '. + {($n): $s}')
+          fi
+        fi
+      done
+      updated_oc="$existing_oc"
+    fi
+
+    local opencode_base final_opencode
+    opencode_base=$(cat "$opencode_file")
+    final_opencode=$(printf '%s' "$opencode_base" | jq --argjson mcp "$updated_oc" '. + {mcp: $mcp}')
+    write_json "$opencode_file" "$final_opencode"
+    echo "  ✔  Seeded ${#server_names[@]} server(s) to opencode.json (strategy: $strategy)"
+  fi
+
+  # ── Seed .gemini/settings.json (Gemini) ──────────────────────────────────
+  local gemini_file="$TARGET/.gemini/settings.json"
+  if [[ -f "$gemini_file" ]]; then
+    local existing_gs updated_gs
+    existing_gs=$(jq '.mcpServers // {}' "$gemini_file" 2>/dev/null || echo "{}")
+
+    if [[ "$strategy" == "replace" ]]; then
+      updated_gs="{}"
+      local name
+      for name in "${server_names[@]}"; do
+        local server_json gs_entry
+        server_json=$(yq -o json ".mcp.servers.$name" "$profile_file" 2>/dev/null || echo "{}")
+        if [[ -n "$server_json" && "$server_json" != "null" ]]; then
+          gs_entry=$(translate_to_gemini "$server_json")
+          updated_gs=$(printf '%s' "$updated_gs" | jq --arg n "$name" --argjson s "$gs_entry" '. + {($n): $s}')
+        fi
+      done
+    else
+      # Merge: add only if key doesn't already exist
+      local name
+      for name in "${server_names[@]}"; do
+        local exists
+        exists=$(printf '%s' "$existing_gs" | jq -r --arg n "$name" 'has($n)')
+        if [[ "$exists" == "false" ]]; then
+          local server_json gs_entry
+          server_json=$(yq -o json ".mcp.servers.$name" "$profile_file" 2>/dev/null || echo "{}")
+          if [[ -n "$server_json" && "$server_json" != "null" ]]; then
+            gs_entry=$(translate_to_gemini "$server_json")
+            existing_gs=$(printf '%s' "$existing_gs" | jq --arg n "$name" --argjson s "$gs_entry" '. + {($n): $s}')
+          fi
+        fi
+      done
+      updated_gs="$existing_gs"
+    fi
+
+    local gemini_base final_gemini
+    gemini_base=$(cat "$gemini_file")
+    final_gemini=$(printf '%s' "$gemini_base" | jq --argjson mcpServers "$updated_gs" '. + {mcpServers: $mcpServers}')
+    write_json "$gemini_file" "$final_gemini"
+    echo "  ✔  Seeded ${#server_names[@]} server(s) to .gemini/settings.json (strategy: $strategy)"
+  fi
+}
+
 # ── Dispatch ──────────────────────────────────────────────────────────────────
 case "$ACTION" in
   add)    action_add    ;;
   remove) action_remove ;;
   list)   action_list   ;;
-  *) echo "Error: unknown action '$ACTION' (expected add|remove|list)" >&2; exit 1 ;;
+  seed)
+    # Non-interactive seed from profile - uses globally parsed PROFILE_FILE and STRATEGY
+    # Set defaults if not provided
+    [[ -z "$PROFILE_FILE" ]] && { echo "Error: --profile-file required for seed action" >&2; exit 1; }
+    [[ -f "$PROFILE_FILE" ]] || { echo "Error: profile file not found: $PROFILE_FILE" >&2; exit 1; }
+    [[ -z "$TARGET" ]] && { echo "Error: --target required for seed action" >&2; exit 1; }
+
+    # Use default strategy if not provided
+    [[ -z "$STRATEGY" ]] && STRATEGY="merge"
+
+    action_seed "$PROFILE_FILE" "$STRATEGY"
+    ;;
+  *) echo "Error: unknown action '$ACTION' (expected add|remove|list|seed)" >&2; exit 1 ;;
 esac
diff --git a/tooling/lib/test.sh b/tooling/lib/test.sh
index d157f92..1dce477 100755
--- a/tooling/lib/test.sh
+++ b/tooling/lib/test.sh
@@ -1095,6 +1095,249 @@ assert_stdout_contains "$T57_OUTPUT" "--dir" "T57"
 assert_stdout_contains "$T57_OUTPUT" "--global" "T57"
 assert_stdout_contains "$T57_OUTPUT" "--branch" "T57"
 
+# ══════════════════════════════════════════════════════════════════════════════
+# MCP SERVER SEEDING TESTS (profile mcp: key)
+# ══════════════════════════════════════════════════════════════════════════════
+
+MCP="$LIBRARY/tooling/lib/mcp.sh"
+
+# T67 — compose: MCP seed creates .mcp.json with correct keys
+run_test "T67 — compose: MCP seed creates .mcp.json"
+# Create a profile with mcp.servers
+mkdir -p "$TMP/t67"
+cat > "$TMP/t67-profile.yaml" <<'EOF'
+meta:
+  name: Test MCP Profile
+  description: Test profile with MCP servers
+  version: "1.0.0"
+fragments:
+  base:
+    - git-conventions
+output:
+  build_command: ""
+  test_command: ""
+  lint_command: ""
+vendors:
+  enabled: []
+mcp:
+  strategy: merge
+  servers:
+    github:
+      type: stdio
+      command: npx
+      args: ["-y", "@modelcontextprotocol/server-github"]
+    postgres:
+      type: stdio
+      command: npx
+      args: ["-y", "@modelcontextprotocol/server-postgres"]
+      env:
+        DATABASE_URL: "postgresql://localhost:5432"
+EOF
+
+bash "$COMPOSE" \
+  --library "$LIBRARY" \
+  --profile-file "$TMP/t67-profile.yaml" \
+  --target "$TMP/t67" \
+  > /dev/null 2>&1
+
+assert_file_exists "$TMP/t67/.mcp.json" "T67"
+assert_json_valid "$TMP/t67/.mcp.json" "T67"
+assert_file_contains "$TMP/t67/.mcp.json" "github" "T67"
+assert_file_contains "$TMP/t67/.mcp.json" "postgres" "T67"
+assert_file_contains "$TMP/t67/.mcp.json" '"command": "npx"' "T67"
+
+# T68 — compose: MCP seed writes to opencode.json with translations
+run_test "T68 — compose: MCP seed translates for opencode.json"
+mkdir -p "$TMP/t68"
+# Create opencode.json first (simulating existing vendor)
+echo '{"mcp":{}}' > "$TMP/t68/opencode.json"
+
+cat > "$TMP/t68-profile.yaml" <<'EOF'
+meta:
+  name: Test MCP Opencode
+  description: Test profile with MCP servers for opencode
+  version: "1.0.0"
+fragments:
+  base:
+    - git-conventions
+output:
+  build_command: ""
+  test_command: ""
+  lint_command: ""
+vendors:
+  enabled: []
+mcp:
+  servers:
+    test-server:
+      type: stdio
+      command: npx
+      args: ["-y", "some-server"]
+      env:
+        MY_TOKEN: "${MY_TOKEN}"
+EOF
+
+bash "$COMPOSE" \
+  --library "$LIBRARY" \
+  --profile-file "$TMP/t68-profile.yaml" \
+  --target "$TMP/t68" \
+  > /dev/null 2>&1
+
+assert_file_exists "$TMP/t68/opencode.json" "T68"
+assert_file_contains "$TMP/t68/opencode.json" '"local"' "T68"
+assert_file_contains "$TMP/t68/opencode.json" '"environment"' "T68"
+
+# T69 — compose: MCP seed writes to .gemini/settings.json without type field
+run_test "T69 — compose: MCP seed translates for .gemini/settings.json"
+mkdir -p "$TMP/t69/.gemini"
+echo '{"mcpServers":{}}' > "$TMP/t69/.gemini/settings.json"
+
+cat > "$TMP/t69-profile.yaml" <<'EOF'
+meta:
+  name: Test MCP Gemini
+  description: Test profile with MCP servers for gemini
+  version: "1.0.0"
+fragments:
+  base:
+    - git-conventions
+output:
+  build_command: ""
+  test_command: ""
+  lint_command: ""
+vendors:
+  enabled: []
+mcp:
+  servers:
+    http-server:
+      type: http
+      url: "http://localhost:3000"
+EOF
+
+bash "$COMPOSE" \
+  --library "$LIBRARY" \
+  --profile-file "$TMP/t69-profile.yaml" \
+  --target "$TMP/t69" \
+  > /dev/null 2>&1
+
+assert_file_exists "$TMP/t69/.gemini/settings.json" "T69"
+assert_file_contains "$TMP/t69/.gemini/settings.json" "http-server" "T69"
+assert_file_contains "$TMP/t69/.gemini/settings.json" "httpUrl" "T69"
+# Should NOT contain 'type' field
+assert_file_not_contains "$TMP/t69/.gemini/settings.json" '"type"' "T69"
+
+# T70 — compose: MCP merge strategy preserves existing servers
+run_test "T70 — compose: MCP merge preserves existing servers"
+mkdir -p "$TMP/t70"
+# Pre-existing .mcp.json with a server
+echo '{"mcpServers":{"existing-server":{"type":"stdio","command":"echo","args":["hello"]}}}' > "$TMP/t70/.mcp.json"
+
+cat > "$TMP/t70-profile.yaml" <<'EOF'
+meta:
+  name: Test MCP Merge
+  description: Test profile with MCP servers merge
+  version: "1.0.0"
+fragments:
+  base:
+    - git-conventions
+output:
+  build_command: ""
+  test_command: ""
+  lint_command: ""
+vendors:
+  enabled: []
+mcp:
+  strategy: merge
+  servers:
+    new-server:
+      type: stdio
+      command: echo
+      args: ["new"]
+EOF
+
+bash "$COMPOSE" \
+  --library "$LIBRARY" \
+  --profile-file "$TMP/t70-profile.yaml" \
+  --target "$TMP/t70" \
+  > /dev/null 2>&1
+
+assert_file_contains "$TMP/t70/.mcp.json" "existing-server" "T70"
+assert_file_contains "$TMP/t70/.mcp.json" "new-server" "T70"
+
+# T71 — compose: MCP replace strategy removes old servers
+run_test "T71 — compose: MCP replace removes old servers"
+mkdir -p "$TMP/t71"
+echo '{"mcpServers":{"old-server":{"type":"stdio","command":"old","args":["old"]}}}' > "$TMP/t71/.mcp.json"
+
+cat > "$TMP/t71-profile.yaml" <<'EOF'
+meta:
+  name: Test MCP Replace
+  description: Test profile with MCP servers replace
+  version: "1.0.0"
+fragments:
+  base:
+    - git-conventions
+output:
+  build_command: ""
+  test_command: ""
+  lint_command: ""
+vendors:
+  enabled: []
+mcp:
+  strategy: replace
+  servers:
+    brand-new:
+      type: http
+      url: "http://localhost:8080"
+EOF
+
+bash "$COMPOSE" \
+  --library "$LIBRARY" \
+  --profile-file "$TMP/t71-profile.yaml" \
+  --target "$TMP/t71" \
+  > /dev/null 2>&1
+
+assert_file_contains "$TMP/t71/.mcp.json" "brand-new" "T71"
+assert_file_not_contains "$TMP/t71/.mcp.json" "old-server" "T71"
+
+# T72 — compose: profile without mcp key produces no MCP files
+run_test "T72 — compose: profile without mcp key is no-op"
+mkdir -p "$TMP/t72"
+
+cat > "$TMP/t72-profile.yaml" <<'EOF'
+meta:
+  name: Test No MCP
+  description: Test profile without MCP servers
+  version: "1.0.0"
+fragments:
+  base:
+    - git-conventions
+output:
+  build_command: ""
+  test_command: ""
+  lint_command: ""
+vendors:
+  enabled: []
+EOF
+
+bash "$COMPOSE" \
+  --library "$LIBRARY" \
+  --profile-file "$TMP/t72-profile.yaml" \
+  --target "$TMP/t72" \
+  > /dev/null 2>&1
+
+# Should not touch vendor MCP files (none should exist)
+assert_file_not_exists "$TMP/t72/.mcp.json" "T72"
+assert_file_not_exists "$TMP/t72/opencode.json" "T72"
+assert_file_not_exists "$TMP/t72/.gemini/settings.json" "T72"
+
+# T73 — lint: schema validation passes with mcp key
+run_test "T73 — lint: schema validation passes with mcp key"
+T73_EXIT=0
+bash "$LINT" \
+  --library "$LIBRARY" \
+  > /dev/null 2>&1 || T73_EXIT=$?
+
+assert_exit_code 0 "$T73_EXIT" "T73"
+
 # ══════════════════════════════════════════════════════════════════════════════
 # INDEX STABILITY TESTS
 # ══════════════════════════════════════════════════════════════════════════════