diff --git a/mateclaw-server/src/main/java/vip/mate/tool/builtin/DocxRenderTool.java b/mateclaw-server/src/main/java/vip/mate/tool/builtin/DocxRenderTool.java
index 734646e2..fb47a871 100644
--- a/mateclaw-server/src/main/java/vip/mate/tool/builtin/DocxRenderTool.java
+++ b/mateclaw-server/src/main/java/vip/mate/tool/builtin/DocxRenderTool.java
@@ -7,6 +7,11 @@ import org.springframework.ai.tool.annotation.ToolParam;
 import org.springframework.stereotype.Component;
 import vip.mate.tool.document.GeneratedFileCache;
 import vip.mate.tool.document.MarkdownDocxRenderer;
+import vip.mate.tool.guard.WorkspacePathGuard;
+
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
 
 /**
  * Render a brand-new .docx from Markdown without ever forking a process.
@@ -83,6 +88,96 @@ public class DocxRenderTool {
         }
     }
 
+    /**
+     * File-based renderer — reads markdown from disk instead of taking it as a
+     * tool argument. Bypasses the LLM token-cost cliff: a 80 KB markdown body
+     * would otherwise be streamed through the chat completion as part of
+     * {@code renderDocx.markdown} args (≈ 20 K tokens, several minutes of
+     * generation just to repeat back content the LLM already wrote to disk).
+     * <p>
+     * Workflow: agent uses {@code write_file} / {@code edit_file} to assemble
+     * the markdown locally → calls this tool with the file path → docx is
+     * rendered from disk in one IO call. Token cost ≈ 50 (just the path).
+     */
+    @Tool(description = """
+        Render a .docx file from a markdown FILE on disk and return a one-time download URL.
+        Use this instead of `renderDocx` when the markdown body is large (>5 KB) — the
+        LLM does not need to repeat its own previous output as a tool argument.
+
+        Typical workflow:
+          1. write_file(path="report.md", content="# Report\\n...")  // assemble markdown
+          2. renderDocxFromFile(filePath="report.md", filename="monthly-report")
+          3. return the download link to the user
+
+        The markdown file is read with UTF-8. Path resolution honors the workspace
+        boundary (same rules as read_file / write_file).
+
+        Same supported markdown subset as renderDocx (headings, bold, lists, tables).
+        Image references (![alt](path)) are NOT yet rendered into the docx — they will
+        appear as raw markdown text. SVG inline embedding requires a follow-up tool.
+        """)
+    public String renderDocxFromFile(
+            @ToolParam(description = "Absolute or workspace-relative path to a markdown file")
+            String filePath,
+            @ToolParam(description = "Output filename without extension, e.g. 'monthly-report'")
+            String filename,
+            @ToolParam(description = "Page size: A4 or LETTER (default: A4)", required = false)
+            String pageSize) {
+
+        if (filePath == null || filePath.isBlank()) {
+            return "Error: filePath parameter is empty.";
+        }
+
+        Path resolved;
+        try {
+            resolved = WorkspacePathGuard.validatePath(filePath);
+        } catch (Exception e) {
+            return "Error: path validation failed — " + e.getMessage();
+        }
+        if (!Files.exists(resolved)) {
+            return "Error: file not found at " + resolved;
+        }
+        if (!Files.isRegularFile(resolved) || !Files.isReadable(resolved)) {
+            return "Error: path is not a readable regular file " + resolved;
+        }
+
+        String markdown;
+        long mdBytes;
+        try {
+            mdBytes = Files.size(resolved);
+            markdown = Files.readString(resolved, StandardCharsets.UTF_8);
+        } catch (Exception e) {
+            log.error("[DocxRender] read markdown failed for {}: {}", resolved, e.getMessage(), e);
+            return "Error: failed to read markdown — " + e.getMessage();
+        }
+        if (markdown.isBlank()) {
+            return "Error: markdown file is empty " + resolved;
+        }
+
+        String safeName = sanitizeFilename(filename);
+        String displayName = safeName + ".docx";
+        String size = (pageSize == null || pageSize.isBlank()) ? "A4" : pageSize.trim();
+
+        try {
+            long t0 = System.currentTimeMillis();
+            byte[] bytes = renderer.render(markdown, size);
+            String id = cache.put(bytes, displayName, DOCX_MIME);
+            long elapsed = System.currentTimeMillis() - t0;
+            log.info("[DocxRender] generated {} ({} bytes from {} bytes md, {}ms, id={})",
+                    displayName, bytes.length, mdBytes, elapsed, id);
+
+            String url = "/api/v1/files/generated/" + id;
+            return "Document generated: [" + displayName + "](" + url + ") (link valid for 10 minutes).\n"
+                    + "IMPORTANT: when replying to the user you **must** use the relative path `"
+                    + url + "` verbatim. Do **not** prepend any https://, http:// or domain — "
+                    + "the frontend will resolve the current host automatically.";
+        } catch (Exception e) {
+            log.error("[DocxRender] render failed for {} (source: {}): {}",
+                    displayName, resolved, e.getMessage(), e);
+            return "Render failed: " + e.getMessage();
+        }
+    }
+
     /**
      * Strip path separators and other unsafe characters from a user-supplied
      * filename. Falls back to a generic name when nothing usable remains.