diff --git a/CHANGELOG.md b/CHANGELOG.md
index 34565d9463..870b3a5b62 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -35,6 +35,8 @@
 
 - **combo (per-model-quota providers exhausted on a single model 500):** for per-model-quota providers (gemini, github, passthrough, compatible) that multiplex many models behind one connection, a model-level `500` (e.g. Gemini "Internal error encountered") wrongly marked the whole connection exhausted, so sibling models on the same connection were skipped and the combo could 502 instead of falling back. `markConnectionLevelExhaustion` now leaves the connection eligible on a `500` for per-model-quota providers (other connection-level statuses — 408/502/503/504/524 — still exhaust correctly), and the retry loop early-returns when a model is already in lockout. Regression guard: `tests/unit/combo/combo-target-exhaustion.test.ts`. ([#5976](https://github.com/diegosouzapw/OmniRoute/pull/5976) — thanks @hartmark)
 
+- fix(providers): GitLab Duo executor now emulates OpenAI tool_calls (#6051)
+
 ### 📝 Maintenance
 
 - **ci (env-doc base-red):** document `BIFROST_PORT` in `.env.example` + `docs/reference/ENVIRONMENT.md`. The Bifrost embedded-service merge referenced `process.env.BIFROST_PORT` (`src/lib/services/bootstrap.ts`, default `8080`) without documenting it, so `check:env-doc-sync` failed on the release tip — reddening the `Fast Quality Gates` job for **every** open PR→release regardless of its content. Docs-only; no runtime change.
diff --git a/open-sse/executors/gitlab.ts b/open-sse/executors/gitlab.ts
index 9ccec9a46b..888e10b94a 100644
--- a/open-sse/executors/gitlab.ts
+++ b/open-sse/executors/gitlab.ts
@@ -10,6 +10,13 @@ import {
 } from "./base.ts";
 import { FETCH_TIMEOUT_MS } from "../config/constants.ts";
 import { getAccessToken } from "../services/tokenRefresh.ts";
+import { prepareToolMessages, buildToolAwareResult } from "../translator/webTools.ts";
+import {
+  buildStreamingResponse,
+  buildJsonCompletion,
+  buildToolJsonCompletion,
+  buildToolStreamingResponse,
+} from "./gitlabResponses.ts";
 import {
   buildGitLabDirectGatewayUrl,
   buildGitLabOAuthEndpoints,
@@ -112,101 +119,6 @@ function toOpenAIError(status: number, message: string): Response {
   );
 }
 
-function buildSseChunk(data: unknown): string {
-  return `data: ${JSON.stringify(data)}\n\n`;
-}
-
-function buildStreamingResponse(
-  content: string,
-  model: string,
-  id: string,
-  created: number
-): Response {
-  const encoder = new TextEncoder();
-
-  const body = new ReadableStream<Uint8Array>({
-    start(controller) {
-      controller.enqueue(
-        encoder.encode(
-          buildSseChunk({
-            id,
-            object: "chat.completion.chunk",
-            created,
-            model,
-            choices: [{ index: 0, delta: { role: "assistant" }, finish_reason: null }],
-          })
-        )
-      );
-
-      if (content) {
-        controller.enqueue(
-          encoder.encode(
-            buildSseChunk({
-              id,
-              object: "chat.completion.chunk",
-              created,
-              model,
-              choices: [{ index: 0, delta: { content }, finish_reason: null }],
-            })
-          )
-        );
-      }
-
-      controller.enqueue(
-        encoder.encode(
-          buildSseChunk({
-            id,
-            object: "chat.completion.chunk",
-            created,
-            model,
-            choices: [{ index: 0, delta: {}, finish_reason: "stop" }],
-          })
-        )
-      );
-      controller.enqueue(encoder.encode("data: [DONE]\n\n"));
-      controller.close();
-    },
-  });
-
-  return new Response(body, {
-    status: 200,
-    headers: { "Content-Type": "text/event-stream" },
-  });
-}
-
-function buildJsonCompletion(
-  content: string,
-  model: string,
-  id: string,
-  created: number
-): Response {
-  const estimated = Math.max(1, Math.ceil(content.length / 4));
-  return new Response(
-    JSON.stringify({
-      id,
-      object: "chat.completion",
-      created,
-      model,
-      choices: [
-        {
-          index: 0,
-          message: { role: "assistant", content },
-          finish_reason: "stop",
-        },
-      ],
-      usage: {
-        prompt_tokens: estimated,
-        completion_tokens: estimated,
-        total_tokens: estimated * 2,
-      },
-    }),
-    {
-      status: 200,
-      headers: { "Content-Type": "application/json" },
-    }
-  );
-}
-
 function mergeCredentials(
   current: ProviderCredentials,
   patch: Partial<ProviderCredentials> | null | undefined
@@ -572,9 +484,20 @@ export class GitlabExecutor extends BaseExecutor {
   }
 
   async execute(input: ExecuteInput) {
-    const prompt = buildPrompt(
-      (input.body as Record<string, unknown>)?.messages as OpenAIMessage[]
+    const bodyObj = (input.body as Record<string, unknown>) || {};
+    const rawMessages = (bodyObj.messages as OpenAIMessage[]) || [];
+
+    // Emulate OpenAI tool calling for GitLab Duo (which has no native function
+    // calling). When `tools` are present we serialize the tool contract into the
+    // prompt and parse `<tool>{...}</tool>` blocks back out of the completion text
+    // into OpenAI `tool_calls` — the same web-tool-emulation idiom used by the
+    // qwen-web / duckduckgo-web executors (#6051).
+    const { hasTools, requestedTools, effectiveMessages } = prepareToolMessages(
+      bodyObj,
+      rawMessages as Array<{ role: string; content: unknown }>
     );
+
+    const prompt = buildPrompt(effectiveMessages as OpenAIMessage[]);
     if (!prompt) {
       return {
         response: toOpenAIError(400, "GitLab Duo requires at least one user message"),
@@ -598,7 +521,7 @@ export class GitlabExecutor extends BaseExecutor {
 
     const transformedBody = this.transformRequest(
       input.model,
-      (input.body as Record<string, unknown>) || {},
+      { ...bodyObj, messages: effectiveMessages },
       false,
       activeCredentials
     );
@@ -684,6 +607,24 @@ export class GitlabExecutor extends BaseExecutor {
     const resolvedModel = resolveResponseModel(payload, input.model);
     const responseId = `chatcmpl-gitlab-${randomUUID()}`;
     const created = Math.floor(Date.now() / 1000);
+
+    if (hasTools) {
+      const {
+        content: toolContent,
+        toolCalls,
+        finishReason,
+      } = buildToolAwareResult(content, requestedTools, "gitlab");
+      const message: Record<string, unknown> = { role: "assistant", content: toolContent };
+      if (toolCalls) {
+        message.tool_calls = toolCalls;
+        message.content = null;
+      }
+      const response = input.stream
+        ? buildToolStreamingResponse(message, finishReason, resolvedModel, responseId, created)
+        : buildToolJsonCompletion(message, finishReason, resolvedModel, responseId, created);
+      return { response, url: activeTarget.url, headers: requestHeaders, transformedBody };
+    }
+
     const response = input.stream
       ? buildStreamingResponse(content, resolvedModel, responseId, created)
       : buildJsonCompletion(content, resolvedModel, responseId, created);
diff --git a/open-sse/executors/gitlabResponses.ts b/open-sse/executors/gitlabResponses.ts
new file mode 100644
index 0000000000..0e98bb216c
--- /dev/null
+++ b/open-sse/executors/gitlabResponses.ts
@@ -0,0 +1,191 @@
+// OpenAI-shaped response builders for the GitLab Duo executor. Extracted from
+// gitlab.ts (leaf module — must not import from gitlab.ts) so the executor stays
+// under the file-size cap. Covers plain text (streaming + JSON) and the
+// tool_calls emulation variants added for #6051.
+
+function buildSseChunk(data: unknown): string {
+  return `data: ${JSON.stringify(data)}\n\n`;
+}
+
+export function buildStreamingResponse(
+  content: string,
+  model: string,
+  id: string,
+  created: number
+): Response {
+  const encoder = new TextEncoder();
+
+  const body = new ReadableStream<Uint8Array>({
+    start(controller) {
+      controller.enqueue(
+        encoder.encode(
+          buildSseChunk({
+            id,
+            object: "chat.completion.chunk",
+            created,
+            model,
+            choices: [{ index: 0, delta: { role: "assistant" }, finish_reason: null }],
+          })
+        )
+      );
+
+      if (content) {
+        controller.enqueue(
+          encoder.encode(
+            buildSseChunk({
+              id,
+              object: "chat.completion.chunk",
+              created,
+              model,
+              choices: [{ index: 0, delta: { content }, finish_reason: null }],
+            })
+          )
+        );
+      }
+
+      controller.enqueue(
+        encoder.encode(
+          buildSseChunk({
+            id,
+            object: "chat.completion.chunk",
+            created,
+            model,
+            choices: [{ index: 0, delta: {}, finish_reason: "stop" }],
+          })
+        )
+      );
+      controller.enqueue(encoder.encode("data: [DONE]\n\n"));
+      controller.close();
+    },
+  });
+
+  return new Response(body, {
+    status: 200,
+    headers: { "Content-Type": "text/event-stream" },
+  });
+}
+
+export function buildJsonCompletion(
+  content: string,
+  model: string,
+  id: string,
+  created: number
+): Response {
+  const estimated = Math.max(1, Math.ceil(content.length / 4));
+  return new Response(
+    JSON.stringify({
+      id,
+      object: "chat.completion",
+      created,
+      model,
+      choices: [
+        {
+          index: 0,
+          message: { role: "assistant", content },
+          finish_reason: "stop",
+        },
+      ],
+      usage: {
+        prompt_tokens: estimated,
+        completion_tokens: estimated,
+        total_tokens: estimated * 2,
+      },
+    }),
+    {
+      status: 200,
+      headers: { "Content-Type": "application/json" },
+    }
+  );
+}
+
+export function buildToolJsonCompletion(
+  message: Record<string, unknown>,
+  finishReason: string,
+  model: string,
+  id: string,
+  created: number
+): Response {
+  const contentForEstimate = typeof message.content === "string" ? message.content : "";
+  const estimated = Math.max(1, Math.ceil(contentForEstimate.length / 4));
+  return new Response(
+    JSON.stringify({
+      id,
+      object: "chat.completion",
+      created,
+      model,
+      choices: [
+        {
+          index: 0,
+          message,
+          finish_reason: finishReason,
+        },
+      ],
+      usage: {
+        prompt_tokens: estimated,
+        completion_tokens: estimated,
+        total_tokens: estimated * 2,
+      },
+    }),
+    {
+      status: 200,
+      headers: { "Content-Type": "application/json" },
+    }
+  );
+}
+
+export function buildToolStreamingResponse(
+  message: Record<string, unknown>,
+  finishReason: string,
+  model: string,
+  id: string,
+  created: number
+): Response {
+  const encoder = new TextEncoder();
+
+  const body = new ReadableStream<Uint8Array>({
+    start(controller) {
+      controller.enqueue(
+        encoder.encode(
+          buildSseChunk({
+            id,
+            object: "chat.completion.chunk",
+            created,
+            model,
+            choices: [{ index: 0, delta: { role: "assistant" }, finish_reason: null }],
+          })
+        )
+      );
+
+      controller.enqueue(
+        encoder.encode(
+          buildSseChunk({
+            id,
+            object: "chat.completion.chunk",
+            created,
+            model,
+            choices: [{ index: 0, delta: message, finish_reason: null }],
+          })
+        )
+      );
+
+      controller.enqueue(
+        encoder.encode(
+          buildSseChunk({
+            id,
+            object: "chat.completion.chunk",
+            created,
+            model,
+            choices: [{ index: 0, delta: {}, finish_reason: finishReason }],
+          })
+        )
+      );
+      controller.enqueue(encoder.encode("data: [DONE]\n\n"));
+      controller.close();
+    },
+  });
+
+  return new Response(body, {
+    status: 200,
+    headers: { "Content-Type": "text/event-stream" },
+  });
+}
diff --git a/tests/unit/gitlab-duo-toolcalls-6051.test.ts b/tests/unit/gitlab-duo-toolcalls-6051.test.ts
new file mode 100644
index 0000000000..3bf8df51ef
--- /dev/null
+++ b/tests/unit/gitlab-duo-toolcalls-6051.test.ts
@@ -0,0 +1,145 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { GitlabExecutor } from "../../open-sse/executors/gitlab.ts";
+
+function jsonResponse(body: unknown, status = 200) {
+  return new Response(JSON.stringify(body), {
+    status,
+    headers: { "Content-Type": "application/json" },
+  });
+}
+
+const WEATHER_TOOL = {
+  type: "function",
+  function: {
+    name: "get_weather",
+    description: "Get the current weather for a city",
+    parameters: {
+      type: "object",
+      properties: { city: { type: "string" } },
+      required: ["city"],
+    },
+  },
+};
+
+test("GitlabExecutor emulates OpenAI tool_calls when body.tools is present (#6051)", async () => {
+  const executor = new GitlabExecutor();
+  const originalFetch = globalThis.fetch;
+  const calls: Array<{ url: string; body: Record<string, unknown> }> = [];
+
+  // Upstream (GitLab code_suggestions) replies with the tool invocation as raw
+  // text, exactly how a web/completion model would when handed the tool contract.
+  globalThis.fetch = async (url, init = {}) => {
+    calls.push({ url: String(url), body: JSON.parse(String(init.body || "{}")) });
+    return jsonResponse({
+      model: { name: "code-gecko" },
+      choices: [
+        {
+          text: 'Sure, let me check.\n<tool>{"name": "get_weather", "arguments": {"city": "Paris"}}</tool>',
+        },
+      ],
+    });
+  };
+
+  try {
+    const result = await executor.execute({
+      model: "gitlab-duo-code-suggestions",
+      body: {
+        messages: [{ role: "user", content: "What's the weather in Paris?" }],
+        tools: [WEATHER_TOOL],
+        tool_choice: "auto",
+      },
+      stream: false,
+      credentials: { apiKey: "glpat-test" },
+      signal: AbortSignal.timeout(10_000),
+      log: null,
+    } as any);
+
+    // The serialized tool contract must reach the GitLab prompt.
+    assert.equal(calls.length, 1);
+    assert.match(
+      String((calls[0].body.current_file as any)?.content_above_cursor ?? ""),
+      /get_weather/,
+      "tool contract must be serialized into the GitLab prompt"
+    );
+
+    const body = (await result.response.json()) as any;
+    const choice = body.choices[0];
+    assert.equal(choice.finish_reason, "tool_calls");
+    assert.ok(Array.isArray(choice.message.tool_calls), "tool_calls array must be present");
+    assert.equal(choice.message.tool_calls.length, 1);
+    assert.equal(choice.message.tool_calls[0].type, "function");
+    assert.equal(choice.message.tool_calls[0].function.name, "get_weather");
+    assert.deepEqual(JSON.parse(choice.message.tool_calls[0].function.arguments), {
+      city: "Paris",
+    });
+    assert.equal(choice.message.content, null);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});
+
+test("GitlabExecutor streams a tool_calls chunk when tools are present (#6051)", async () => {
+  const executor = new GitlabExecutor();
+  const originalFetch = globalThis.fetch;
+
+  globalThis.fetch = async () =>
+    jsonResponse({
+      model: { name: "code-gecko" },
+      choices: [{ text: '<tool>{"name": "get_weather", "arguments": {"city": "Paris"}}</tool>' }],
+    });
+
+  try {
+    const result = await executor.execute({
+      model: "gitlab-duo-code-suggestions",
+      body: {
+        messages: [{ role: "user", content: "weather in Paris?" }],
+        tools: [WEATHER_TOOL],
+      },
+      stream: true,
+      credentials: { apiKey: "glpat-test" },
+      signal: AbortSignal.timeout(10_000),
+      log: null,
+    } as any);
+
+    assert.equal(result.response.headers.get("Content-Type"), "text/event-stream");
+    const text = await result.response.text();
+    assert.match(text, /"tool_calls"/, "SSE stream must carry a tool_calls delta");
+    assert.match(text, /get_weather/);
+    assert.match(text, /"finish_reason":"tool_calls"/);
+    assert.match(text, /data: \[DONE\]/);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});
+
+test("GitlabExecutor keeps plain-text finish_reason:stop for non-tool requests (#6051)", async () => {
+  const executor = new GitlabExecutor();
+  const originalFetch = globalThis.fetch;
+
+  globalThis.fetch = async () =>
+    jsonResponse({
+      model: { name: "code-gecko" },
+      choices: [{ text: "def hello():\n    return 'world'" }],
+    });
+
+  try {
+    const result = await executor.execute({
+      model: "gitlab-duo-code-suggestions",
+      body: { messages: [{ role: "user", content: "Write a hello world function" }] },
+      stream: false,
+      credentials: { apiKey: "glpat-test" },
+      signal: AbortSignal.timeout(10_000),
+      log: null,
+    } as any);
+
+    const body = (await result.response.json()) as any;
+    const choice = body.choices[0];
+    assert.equal(choice.finish_reason, "stop");
+    assert.equal(choice.message.tool_calls, undefined);
+    assert.match(choice.message.content, /hello/);
+  } finally {
+    globalThis.fetch = originalFetch;
+  }
+});