diff --git a/actions/setup/js/mcp_cli_bridge.cjs b/actions/setup/js/mcp_cli_bridge.cjs
index 9857289f18..d45d124e4a 100644
--- a/actions/setup/js/mcp_cli_bridge.cjs
+++ b/actions/setup/js/mcp_cli_bridge.cjs
@@ -457,6 +457,24 @@ function hasStdinPlaceholder(args) {
   return false;
 }
 
+/**
+ * Check whether stdin should be read and parsed as a JSON payload for tool arguments.
+ * Returns true when the '.' sentinel is the only argument, or when no arguments are
+ * provided and stdin is not connected to a terminal (i.e. data is being piped).
+ *
+ * This enables agents to pipe complex multi-argument payloads as a single JSON object:
+ *   printf '{"issue_number":42,"body":"hello"}' | safeoutputs add_comment .
+ *   printf '{"issue_number":42,"body":"hello"}' | safeoutputs add_comment
+ *
+ * @param {string[]} args - User arguments after the tool name
+ * @returns {boolean}
+ */
+function hasStdinJsonPayload(args) {
+  if (args.length === 1 && args[0] === ".") return true;
+  if (args.length === 0 && !process.stdin.isTTY) return true;
+  return false;
+}
+
 /** Maximum bytes accepted from stdin to prevent memory exhaustion (10 MB) */
 const STDIN_MAX_BYTES = 10 * 1024 * 1024;
 
@@ -508,6 +526,12 @@ function readStdinSync() {
  * content is substituted in place of that value. This allows multiline
  * strings to be piped safely: `printf 'line1\nline2' | cmd --body -`
  *
+ * When `stdinContent` is provided and args is empty or `['.']`, the stdin
+ * content is parsed as a JSON object and its properties are used as tool
+ * arguments directly (JSON payload mode). This enables agents to pipe
+ * complex multi-argument payloads without shell quoting issues:
+ *   printf '{"issue_number":42,"body":"hello"}' | safeoutputs add_comment .
+ *
  * @param {string[]} args - User arguments after the tool name
  * @param {Record<string, {type?: string|string[]}>} [schemaProperties] - Tool input schema properties
  * @param {string | null} [stdinContent] - Pre-read stdin content; substituted when value is '-'
@@ -520,6 +544,26 @@ function parseToolArgs(args, schemaProperties = {}, stdinContent = null) {
   const hasSchemaProperties = Object.keys(schemaProperties).length > 0;
   const { normalizedSchemaKeyMap, ambiguousNormalizedSchemaKeys } = buildNormalizedSchemaKeyMap(schemaProperties);
 
+  // JSON payload mode: when args is empty or ['.'] and stdinContent is available,
+  // parse stdin as a JSON object and use its properties directly as tool arguments.
+  if (stdinContent !== null && (args.length === 0 || (args.length === 1 && args[0] === "."))) {
+    const trimmed = stdinContent.trim();
+    if (trimmed) {
+      try {
+        const parsed = JSON.parse(trimmed);
+        if (parsed !== null && typeof parsed === "object" && !Array.isArray(parsed)) {
+          for (const [key, value] of Object.entries(parsed)) {
+            const canonicalKey = resolveSchemaPropertyKey(key, schemaProperties, normalizedSchemaKeyMap, ambiguousNormalizedSchemaKeys);
+            result[canonicalKey] = value;
+          }
+          return { args: result, json: false };
+        }
+      } catch {
+        // Not valid JSON; fall through to normal flag-based argument parsing.
+      }
+    }
+  }
+
   for (let i = 0; i < args.length; i++) {
     if (args[i].startsWith("--")) {
       const raw = args[i].slice(2);
@@ -1042,10 +1086,12 @@ async function main() {
   const matchedTool = tools.find(tool => tool && typeof tool === "object" && tool.name === toolName);
   const schemaProperties = matchedTool && matchedTool.inputSchema && matchedTool.inputSchema.properties ? matchedTool.inputSchema.properties : {};
 
-  // Pre-read stdin once when any argument uses '-' as a stdin placeholder.
+  // Pre-read stdin once when any argument uses '-' as a stdin placeholder, or when
+  // the JSON payload mode is triggered ('.' sentinel or no args with piped stdin).
   // This avoids shell escaping issues with multiline strings:
   //   printf 'line1\nline2' | safeoutputs add_comment --body -
-  const stdinContent = hasStdinPlaceholder(toolUserArgs) ? readStdinSync() : null;
+  //   printf '{"issue_number":42,"body":"hello"}' | safeoutputs add_comment .
+  const stdinContent = hasStdinPlaceholder(toolUserArgs) || hasStdinJsonPayload(toolUserArgs) ? readStdinSync() : null;
   const { args: toolArgs, json: jsonOutput } = parseToolArgs(toolUserArgs, schemaProperties, stdinContent);
 
   core.info(`[${serverName}] Calling tool '${toolName}' with args: ${JSON.stringify(toolArgs)}${jsonOutput ? " (--json)" : ""}`);
@@ -1105,6 +1151,7 @@ module.exports = {
   renderProgressMessages,
   formatResponse,
   hasStdinPlaceholder,
+  hasStdinJsonPayload,
   readStdinSync,
   main,
 };
diff --git a/actions/setup/js/mcp_cli_bridge.test.cjs b/actions/setup/js/mcp_cli_bridge.test.cjs
index 0bb488bed9..746026012f 100644
--- a/actions/setup/js/mcp_cli_bridge.test.cjs
+++ b/actions/setup/js/mcp_cli_bridge.test.cjs
@@ -1,6 +1,6 @@
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 
-import { formatResponse, hasStdinPlaceholder, parseToolArgs, readStdinSync } from "./mcp_cli_bridge.cjs";
+import { formatResponse, hasStdinPlaceholder, hasStdinJsonPayload, parseToolArgs, readStdinSync } from "./mcp_cli_bridge.cjs";
 
 describe("mcp_cli_bridge.cjs", () => {
   let originalCore;
@@ -338,4 +338,124 @@ describe("mcp_cli_bridge.cjs", () => {
       }
     });
   });
+
+  describe("stdin JSON payload support", () => {
+    it("returns true for '.' sentinel", () => {
+      expect(hasStdinJsonPayload(["."])).toBe(true);
+    });
+
+    it("returns true for empty args when stdin is not a TTY", () => {
+      const origIsTTY = process.stdin.isTTY;
+      process.stdin.isTTY = undefined;
+      try {
+        expect(hasStdinJsonPayload([])).toBe(true);
+      } finally {
+        process.stdin.isTTY = origIsTTY;
+      }
+    });
+
+    it("returns false for empty args when stdin is a TTY", () => {
+      const origIsTTY = process.stdin.isTTY;
+      // @ts-ignore
+      process.stdin.isTTY = true;
+      try {
+        expect(hasStdinJsonPayload([])).toBe(false);
+      } finally {
+        process.stdin.isTTY = origIsTTY;
+      }
+    });
+
+    it("returns false when args contain flags", () => {
+      expect(hasStdinJsonPayload(["--body", "hello"])).toBe(false);
+    });
+
+    it("returns false when args has more than just '.'", () => {
+      expect(hasStdinJsonPayload([".", "--extra", "value"])).toBe(false);
+    });
+
+    it("parses stdin JSON object when '.' sentinel is used", () => {
+      const schemaProperties = {
+        issue_number: { type: "integer" },
+        body: { type: "string" },
+      };
+      const stdinContent = '{"issue_number": 42, "body": "hello world"}';
+
+      const { args } = parseToolArgs(["."], schemaProperties, stdinContent);
+
+      expect(args).toEqual({ issue_number: 42, body: "hello world" });
+    });
+
+    it("parses stdin JSON object when no args and stdinContent is provided", () => {
+      const schemaProperties = {
+        issue_number: { type: "integer" },
+        body: { type: "string" },
+      };
+      const stdinContent = '{"issue_number": 7, "body": "test body"}';
+
+      const { args } = parseToolArgs([], schemaProperties, stdinContent);
+
+      expect(args).toEqual({ issue_number: 7, body: "test body" });
+    });
+
+    it("preserves types from JSON payload without coercion", () => {
+      const schemaProperties = {
+        count: { type: "integer" },
+        enabled: { type: "boolean" },
+        tags: { type: "array" },
+      };
+      const stdinContent = '{"count": 5, "enabled": true, "tags": ["a", "b"]}';
+
+      const { args } = parseToolArgs(["."], schemaProperties, stdinContent);
+
+      expect(args).toEqual({ count: 5, enabled: true, tags: ["a", "b"] });
+    });
+
+    it("normalizes dashed JSON keys to schema underscore keys", () => {
+      const schemaProperties = {
+        issue_number: { type: "integer" },
+      };
+      const stdinContent = '{"issue-number": 99}';
+
+      const { args } = parseToolArgs(["."], schemaProperties, stdinContent);
+
+      expect(args).toEqual({ issue_number: 99 });
+    });
+
+    it("falls through to empty args when stdinContent is null and sentinel is used", () => {
+      const { args } = parseToolArgs(["."], {}, null);
+
+      expect(args).toEqual({});
+    });
+
+    it("falls through to empty args when stdinContent is empty string", () => {
+      const { args } = parseToolArgs(["."], {}, "");
+
+      expect(args).toEqual({});
+    });
+
+    it("falls through to normal parsing when stdinContent is not valid JSON", () => {
+      const schemaProperties = { body: { type: "string" } };
+
+      const { args } = parseToolArgs(["."], schemaProperties, "not json at all");
+
+      expect(args).toEqual({});
+    });
+
+    it("falls through when JSON is an array rather than an object", () => {
+      const { args } = parseToolArgs(["."], {}, '["a","b","c"]');
+
+      expect(args).toEqual({});
+    });
+
+    it("handles multiline JSON payload", () => {
+      const schemaProperties = { body: { type: "string" } };
+      const stdinContent = `{
+  "body": "### Title\\n\\nLine one.\\n\\nLine two."
+}`;
+
+      const { args } = parseToolArgs(["."], schemaProperties, stdinContent);
+
+      expect(args).toEqual({ body: "### Title\n\nLine one.\n\nLine two." });
+    });
+  });
 });
diff --git a/actions/setup/md/mcp_cli_tools_prompt.md b/actions/setup/md/mcp_cli_tools_prompt.md
index c40547eacd..61a37ba8e1 100644
--- a/actions/setup/md/mcp_cli_tools_prompt.md
+++ b/actions/setup/md/mcp_cli_tools_prompt.md
@@ -44,27 +44,55 @@ mcpscripts --help                                  # list all script tools
 mcpscripts mcpscripts-gh --args "pr list --repo owner/repo --limit 5"
 ```
 
-### Multiline String Arguments (stdin piping)
+### Multiline and Multi-Argument Payloads (JSON stdin)
 
-For parameters that contain multiline content (such as `--body` in `add_comment`), use `-` as the value and pipe the content via stdin. This avoids shell quoting and escaping issues:
+**Preferred approach for any tool call with multiple or complex arguments**: pipe a JSON object to the CLI using `.` as the sentinel. The bridge parses stdin as the argument object, preserving all native types (numbers, booleans, arrays) without shell-quoting issues.
+
+```bash
+# Full argument payload as JSON — preferred for multi-argument calls
+printf '{"issue_number":42,"body":"### Title\n\nBody paragraph one.\n\nBody paragraph two."}' \
+  | safeoutputs add_comment .
+
+# Works with any tool — just match the parameter names from <server> <tool> --help
+printf '{"title":"Fix: something","body":"Details here","labels":["bug","priority-high"]}' \
+  | safeoutputs create_issue .
+
+# Pipe from a file
+cat payload.json | safeoutputs add_comment .
+```
+
+> **Why prefer JSON payload mode?**
+> - Single pipe operation for any number of arguments — no repeated `--key value` flags
+> - Native types (integers, booleans, arrays) are preserved exactly as specified
+> - No shell quoting or escaping needed for newlines, quotes, or special characters
+> - Agents can construct the payload as a structured object before emitting the command
+
+Key normalisation rules apply: parameter names with hyphens or underscores are interchangeable (e.g. `issue-number` and `issue_number` both work).
+
+### Single-Parameter stdin Substitution
+
+For the case where only **one** parameter needs multiline content, use `-` as its value:
 
 ```bash
 # Write multiline content to a file and pipe it
-cat body.txt | safeoutputs add_comment --body -
+cat body.txt | safeoutputs add_comment --issue_number 42 --body -
 
-# Or use a here-doc / printf for inline multiline content
-printf '### Title\n\nBody paragraph one.\n\nBody paragraph two.' | safeoutputs add_comment --body -
+# Or use printf for inline multiline content
+printf '### Title\n\nBody paragraph one.\n\nBody paragraph two.' \
+  | safeoutputs add_comment --issue_number 42 --body -
 
 # Works with --key=- form too
-printf 'multiline\ncontent' | safeoutputs add_comment --body=-
+printf 'multiline\ncontent' | safeoutputs add_comment --issue_number 42 --body=-
 ```
 
 > **Important**: Always use stdin piping (`--body -`) instead of command substitution (`--body "$(cat file)"`) when the content contains newlines. Command substitution can strip trailing newlines and cause other quoting problems.
 
 ### Notes
 
-- All parameters are passed as `--name value` pairs; boolean flags can be set with `--flag` (no value) to mean `true`
-- Use `-` as a value to read that parameter from stdin (useful for multiline content)
+- **Prefer JSON payload mode** (`printf '{...}' | server tool .`) for any call with multiple arguments or complex values
+- All parameters can also be passed as `--name value` pairs; boolean flags can be set with `--flag` (no value) to mean `true`
+- Use `.` as the only argument to parse stdin as a JSON object (all parameters supplied at once)
+- Use `-` as a single value to read one parameter from stdin (single-field substitution)
 - Output is printed to stdout; errors are printed to stderr with a non-zero exit code
 - Run the CLI commands inside a `bash` tool call — they are shell executables, not MCP tools
 - These CLI commands are read-only and cannot be modified by the agent