[Docs] Add EBNF to sampling params docs (#2609)

sgl-project · Dec 29, 2024 · fd34f2d · fd34f2d
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diff --git a/docs/backend/openai_api_completions.ipynb b/docs/backend/openai_api_completions.ipynb
@@ -220,14 +220,21 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "## Structured decoding (JSON, Regex)\n",
-    "You can define a JSON schema or regular expression to constrain the model's output. The model output will be guaranteed to follow the given constraints and this depends on the grammar backend.\n",
+    "## Structured Outputs (JSON, Regex, EBNF)\n",
+    "You can specify a JSON schema, Regular Expression or [EBNF](https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form) to constrain the model output. The model output will be guaranteed to follow the given constraints. \n",
     "\n",
-    "SGlang has two backends: [Outlines](https://github.com/dottxt-ai/outlines) (default) and [XGrammar](https://blog.mlc.ai/2024/11/22/achieving-efficient-flexible-portable-structured-generation-with-xgrammar). Xgrammar accelerates JSON decoding performance but does not support regular expressions. To use Xgrammar, add the `--grammar-backend xgrammar` when launching the server:\n",
+    "SGLang supports two grammar backends:\n",
     "\n",
+    "- [Outlines](https://github.com/dottxt-ai/outlines) (default): Supports JSON schema and Regular Expression constraints.\n",
+    "- [XGrammar](https://github.com/mlc-ai/xgrammar): Supports JSON schema and EBNF constraints.\n",
+    "  - XGrammar currently uses the [GGML BNF format](https://github.com/ggerganov/llama.cpp/blob/master/grammars/README.md)\n",
+    "\n",
+    "> 🔔 Only one constraint parameter (`json_schema`, `regex`, or `ebnf`) can be specified at a time.\n",
+    "\n",
+    "Initialise xgrammar backend using `--grammar-backend xgrammar` flag\n",
     "```bash\n",
     "python -m sglang.launch_server --model-path meta-llama/Meta-Llama-3.1-8B-Instruct \\\n",
-    "--port 30000 --host 0.0.0.0 --grammar-backend xgrammar\n",
+    "--port 30000 --host 0.0.0.0 --grammar-backend [xgrammar|outlines] # xgrammar or outlines (default: outlines)\n",
     "```\n",
     "\n",
     "### JSON"
@@ -275,7 +282,7 @@
    "cell_type": "markdown",
    "metadata": {},
    "source": [
-    "### Regular expression"
+    "### Regular expression (use default \"outlines\" backend)"
    ]
   },
   {
@@ -297,6 +304,46 @@
     "print_highlight(response.choices[0].message.content)"
    ]
   },
+  {
+   "cell_type": "markdown",
+   "metadata": {},
+   "source": [
+    "### EBNF (use \"xgrammar\" backend)"
+   ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "metadata": {},
+   "outputs": [],
+   "source": [
+    "# terminate the existing server(that's using default outlines backend) for this demo\n",
+    "terminate_process(server_process)\n",
+    "\n",
+    "# start new server with xgrammar backend\n",
+    "server_process = execute_shell_command(\n",
+    "    \"python -m sglang.launch_server --model-path meta-llama/Meta-Llama-3.1-8B-Instruct --port 30000 --host 0.0.0.0 --grammar-backend xgrammar\"\n",
+    ")\n",
+    "wait_for_server(\"http://localhost:30000\")\n",
+    "\n",
+    "# EBNF example\n",
+    "ebnf_grammar = r\"\"\"\n",
+    "        root ::= \"Hello\" | \"Hi\" | \"Hey\"\n",
+    "        \"\"\"\n",
+    "response = client.chat.completions.create(\n",
+    "    model=\"meta-llama/Meta-Llama-3.1-8B-Instruct\",\n",
+    "    messages=[\n",
+    "        {\"role\": \"system\", \"content\": \"You are a helpful EBNF test bot.\"},\n",
+    "        {\"role\": \"user\", \"content\": \"Say a greeting.\"},\n",
+    "    ],\n",
+    "    temperature=0,\n",
+    "    max_tokens=32,\n",
+    "    extra_body={\"ebnf\": ebnf_grammar},\n",
+    ")\n",
+    "\n",
+    "print_highlight(response.choices[0].message.content)"
+   ]
+  },
   {
    "cell_type": "markdown",
    "metadata": {},

diff --git a/docs/references/sampling_params.md b/docs/references/sampling_params.md
@@ -58,13 +58,18 @@ ignore_eos: bool = False,
 skip_special_tokens: bool = True,
 # Whether to add spaces between special tokens during detokenization.
 spaces_between_special_tokens: bool = True,
-# Constrains the output to follow a given regular expression.
-regex: Optional[str] = None,
 # Do parallel sampling and return `n` outputs.
 n: int = 1,
+
+## Structured Outputs
+# Only one of the below three can be set at a time:
+
+# Constrains the output to follow a given regular expression.
+regex: Optional[str] = None,
 # Constrains the output to follow a given JSON schema.
-# `regex` and `json_schema` cannot be set at the same time.
 json_schema: Optional[str] = None,
+# Constrains the output to follow a given EBNF Grammar.
+ebnf: Optional[str] = None,
 
 ## Penalties. See [Performance Implications on Penalties] section below for more informations.
 
@@ -179,25 +184,37 @@ print(response.json())
 The `image_data` can be a file name, a URL, or a base64 encoded string. See also `python/sglang/srt/utils.py:load_image`.
 Streaming is supported in a similar manner as [above](#streaming).
 
-### Structured decoding (JSON, Regex)
-You can specify a JSON schema or a regular expression to constrain the model output. The model output will be guaranteed to follow the given constraints.
+### Structured Outputs (JSON, Regex, EBNF)
+You can specify a JSON schema, Regular Expression or [EBNF](https://en.wikipedia.org/wiki/Extended_Backus%E2%80%93Naur_form) to constrain the model output. The model output will be guaranteed to follow the given constraints.
+
+SGLang supports two grammar backends:
+
+- [Outlines](https://github.com/dottxt-ai/outlines) (default): Supports JSON schema and Regular Expression constraints.
+- [XGrammar](https://github.com/mlc-ai/xgrammar): Supports JSON schema and EBNF constraints.
+  - XGrammar currently uses the [GGML BNF format](https://github.com/ggerganov/llama.cpp/blob/master/grammars/README.md)
+
+> 🔔 Only one constraint parameter (`json_schema`, `regex`, or `ebnf`) can be specified at a time.
+
+Initialise xgrammar backend using `--grammar-backend xgrammar` flag
+```bash
+python -m sglang.launch_server --model-path meta-llama/Meta-Llama-3.1-8B-Instruct \
+--port 30000 --host 0.0.0.0 --grammar-backend [xgrammar|outlines] # xgrammar or outlines (default: outlines)
+```
 
 ```python
 import json
 import requests
 
-json_schema = json.dumps(
-    {
-        "type": "object",
-        "properties": {
-            "name": {"type": "string", "pattern": "^[\\w]+$"},
-            "population": {"type": "integer"},
-        },
-        "required": ["name", "population"],
-    }
-)
+json_schema = json.dumps({
+    "type": "object",
+    "properties": {
+        "name": {"type": "string", "pattern": "^[\\w]+$"},
+        "population": {"type": "integer"},
+    },
+    "required": ["name", "population"],
+})
 
-# JSON
+# JSON (works with both Outlines and XGrammar)
 response = requests.post(
     "http://localhost:30000/generate",
     json={
@@ -211,7 +228,7 @@ response = requests.post(
 )
 print(response.json())
 
-# Regular expression
+# Regular expression (Outlines backend only)
 response = requests.post(
     "http://localhost:30000/generate",
     json={
@@ -224,4 +241,18 @@ response = requests.post(
     },
 )
 print(response.json())
+
+# EBNF (XGrammar backend only)
+response = requests.post(
+    "http://localhost:30000/generate",
+    json={
+        "text": "Write a greeting.",
+        "sampling_params": {
+            "temperature": 0,
+            "max_new_tokens": 64,
+            "ebnf": 'root ::= "Hello" | "Hi" | "Hey"',
+        },
+    },
+)
+print(response.json())
 ```