diff --git a/model_server/app/commons/constants.py b/model_server/app/commons/constants.py
index d4e01d12..3b937aa5 100644
--- a/model_server/app/commons/constants.py
+++ b/model_server/app/commons/constants.py
@@ -19,6 +19,7 @@
     "top_k": 50,
     "max_tokens": 512,
     "stop_token_ids": [151645],
+    #    "top_logprobs": 10,
 }
 
 arch_guard_model_type = {
@@ -34,3 +35,21 @@
 prompt_guard_dict = loader.get_prompt_guard(arch_guard_model_type[glb.DEVICE])
 
 arch_guard_handler = ArchGuardHanlder(model_dict=prompt_guard_dict)
+# Patterns for function name and parameter parsing
+FUNC_NAME_START_PATTERN = ('<tool_call>\n{"name":"', "<tool_call>\n{'name':'")
+FUNC_NAME_END_TOKEN = ('",', "',")
+
+FIRST_PARAM_NAME_START_PATTERN = ('"arguments":{"', "'arguments':{'")
+PARAMETER_NAME_END_TOKENS = ('":', ':"', "':", ":'")
+PARAMETER_NAME_START_PATTERN = (',"', ",'")
+PARAMETER_VALUE_START_PATTERN = ('":', "':")
+PARAMETER_VALUE_END_TOKEN = ('",', "}}\n", "',")
+
+# Thresholds
+HALLUCINATION_THRESHOLD_DICT = {
+    "t": {"entropy": 0.1, "varentropy": 0.5},
+    "v": {
+        "entropy": 0.5,
+        "varentropy": 2.5,
+    },
+}
diff --git a/model_server/app/function_calling/hallucination_handler.py b/model_server/app/function_calling/hallucination_handler.py
new file mode 100644
index 00000000..eb4a56d1
--- /dev/null
+++ b/model_server/app/function_calling/hallucination_handler.py
@@ -0,0 +1,240 @@
+import json
+import ast
+import os
+import json
+import math
+import torch
+import random
+from typing import Any, Dict, List, Tuple
+import app.commons.constants as const
+import itertools
+
+
+def check_threshold(entropy, varentropy, thd):
+    """
+    Check if the given entropy or variance of entropy exceeds the specified thresholds.
+
+    Args:
+        entropy (float): The entropy value to check.
+        varentropy (float): The variance of entropy value to check.
+        thd (dict): A dictionary containing the threshold values with keys 'entropy' and 'varentropy'.
+
+    Returns:
+        bool: True if either the entropy or varentropy exceeds their respective thresholds, False otherwise.
+    """
+    return entropy > thd["entropy"] or varentropy > thd["varentropy"]
+
+
+def calculate_entropy(log_probs: List[float]) -> Tuple[float, float]:
+    """
+    Calculate the entropy and variance of entropy (varentropy) from log probabilities.
+
+    Args:
+        log_probs (list of float): A list of log probabilities.
+
+    Returns:
+        tuple: A tuple containing:
+            - log_probs (list of float): The input log probabilities as a list.
+            - entropy (float): The calculated entropy.
+            - varentropy (float): The calculated variance of entropy.
+    """
+    log_probs = torch.tensor(log_probs)
+    token_probs = torch.exp(log_probs)
+    entropy = -torch.sum(log_probs * token_probs, dim=-1) / math.log(2, math.e)
+    varentropy = torch.sum(
+        token_probs * (log_probs / math.log(2, math.e)) + entropy.unsqueeze(-1) ** 2,
+        dim=-1,
+    )
+    return entropy.item(), varentropy.item()
+
+
+def check_parameter_property(api_description, parameter_name, property_name):
+    """
+    Check if a parameter in an API description has a specific property.
+
+    Args:
+        api_description (dict): The API description in JSON format.
+        parameter_name (str): The name of the parameter to check.
+        property_name (str): The property to look for (e.g., 'format', 'default').
+
+    Returns:
+        bool: True if the parameter has the specified property, False otherwise.
+    """
+    parameters = api_description.get("properties", {})
+    parameter_info = parameters.get(parameter_name, {})
+
+    return property_name in parameter_info
+
+
+class HallucinationStateHandler:
+    """
+    A class to handle the state of hallucination detection in token processing.
+
+    Attributes:
+        tokens (list): List of tokens processed.
+        logprobs (list): List of log probabilities for each token.
+        state (str): Current state of the handler.
+        mask (list): List of masks indicating the type of each token.
+        parameter_name_done (bool): Flag indicating if parameter name extraction is done.
+        hallucination (bool): Flag indicating if a hallucination is detected.
+        hallucination_message (str): Message describing the hallucination.
+        parameter_name (list): List of extracted parameter names.
+        function_description (dict): Description of functions and their parameters.
+        token_probs_map (list): List mapping tokens to their entropy and variance of entropy.
+        current_token (str): The current token being processed.
+    """
+
+    def __init__(self):
+        """
+        Initializes the HallucinationStateHandler with default values.
+        """
+        self.tokens = []
+        self.logprobs = []
+        self.state = None
+        self.mask = []
+        self.parameter_name_done = False
+        self.hallucination = False
+        self.hallucination_message = ""
+        self.parameter_name = []
+
+        self.token_probs_map = []
+        self.current_token = None
+
+    def process_function(self, apis):
+        self.apis = apis
+        if self.apis is None:
+            raise ValueError("API descriptions not set.")
+        parameter_names = {}
+        for func in self.apis:
+            func_name = func["name"]
+            parameters = func["parameters"]["properties"]
+            parameter_names[func_name] = list(parameters.keys())
+        self.function_description = parameter_names
+        self.function_properties = {x["name"]: x["parameters"] for x in self.apis}
+
+    def process_token(self):
+        """
+        Processes the current token and updates the state and mask accordingly.
+        Detects hallucinations based on the token type and log probabilities.
+        """
+        content = "".join(self.tokens).replace(" ", "")
+        if self.current_token == "<tool_call>":
+            self.mask.append("t")
+            self.check_logprob()
+
+        # Function name extraction logic
+        if self.state == "function_name":
+            if self.current_token not in const.FUNC_NAME_END_TOKEN:
+                self.mask.append("f")
+            else:
+                self.state = None
+                self.check_function_name()
+
+        if content.endswith(const.FUNC_NAME_START_PATTERN):
+            print("function name entered")
+            self.state = "function_name"
+
+        # Parameter name extraction logic
+        if self.state == "parameter_name" and not content.endswith(
+            const.PARAMETER_NAME_END_TOKENS
+        ):
+            self.mask.append("p")
+        elif self.state == "parameter_name" and content.endswith(
+            const.PARAMETER_NAME_END_TOKENS
+        ):
+            self.state = None
+            self.check_parameter_name()
+            self.parameter_name_done = True
+        elif self.parameter_name_done and content.endswith(
+            const.PARAMETER_NAME_START_PATTERN
+        ):
+            self.state = "parameter_name"
+
+        if content.endswith(const.FIRST_PARAM_NAME_START_PATTERN):
+            self.state = "parameter_name"
+
+        # Parameter value extraction logic
+        if self.state == "parameter_value" and not content.endswith(
+            const.PARAMETER_VALUE_END_TOKEN
+        ):
+            if self.current_token.strip() not in ['"', ""]:
+                self.mask.append("v")
+                if (
+                    len(self.mask) > 1
+                    and self.mask[-2] != "v"
+                    and not check_parameter_property(
+                        self.function_properties[self.function_name],
+                        self.parameter_name[-1],
+                        "default",
+                    )
+                ):
+                    self.check_logprob()
+            else:
+                self.mask.append("e")
+
+        elif self.state == "parameter_value" and content.endswith(
+            const.PARAMETER_VALUE_END_TOKEN
+        ):
+            self.state = None
+        elif self.parameter_name_done and content.endswith(
+            const.PARAMETER_VALUE_START_PATTERN
+        ):
+            self.state = "parameter_value"
+
+        # Maintain consistency between stack and mask
+        if len(self.mask) != len(self.tokens):
+            self.mask.append("e")
+
+    def check_logprob(self):
+        """
+        Checks the log probability of the current token and updates the token probability map.
+        Detects hallucinations based on entropy and variance of entropy.
+        """
+        probs = self.logprobs[-1]
+        entropy, varentropy = calculate_entropy(probs)
+        self.token_probs_map.append((self.tokens[-1], entropy, varentropy))
+
+        if check_threshold(
+            entropy, varentropy, const.HALLUCINATION_THRESHOLD_DICT[self.mask[-1]]
+        ):
+            self.hallucination = True
+            self.hallucination_message = f"Token '{self.current_token}' is uncertain."
+
+    def count_consecutive_token(self, token="v") -> int:
+        """
+        Counts the number of consecutive occurrences of a given token in the mask.
+
+        Args:
+            token (str): The token to count in the mask.
+
+        Returns:
+            int: The number of consecutive occurrences of the token.
+        """
+        return (
+            len(list(itertools.takewhile(lambda x: x == token, reversed(self.mask))))
+            if self.mask and self.mask[-1] == token
+            else 0
+        )
+
+    def check_function_name(self):
+        """
+        Checks the extracted function name against the function descriptions.
+        Detects hallucinations if the function name is not found.
+        """
+        f_len = self.count_consecutive_token("f")
+        self.function_name = "".join(self.tokens[:-1][-f_len:])
+        if self.function_name not in self.function_description.keys():
+            self.hallucination = True
+            self.hallucination_message = f"Function name '{self.function_name}' not found in given function descriptions."
+
+    def check_parameter_name(self):
+        """
+        Checks the extracted parameter name against the function descriptions.
+        Detects hallucinations if the parameter name is not found.
+        """
+        p_len = self.count_consecutive_token("p")
+        parameter_name = "".join(self.tokens[:-1][-p_len:])
+        self.parameter_name.append(parameter_name)
+        if parameter_name not in self.function_description[self.function_name]:
+            self.hallucination = True
+            self.hallucination_message = f"Parameter name '{parameter_name}' not found in given function descriptions."
diff --git a/model_server/app/function_calling/model_handler.py b/model_server/app/function_calling/model_handler.py
index 7b915cd4..e1da914c 100644
--- a/model_server/app/function_calling/model_handler.py
+++ b/model_server/app/function_calling/model_handler.py
@@ -134,4 +134,4 @@ def fix_json_string(self, json_str: str):
             fixed_str += opening_bracket[unmatched_opening]
 
         # Attempt to parse the corrected string to ensure it’s valid JSON
-        return fixed_str
+        return fixed_str.replace("'", '"')
diff --git a/model_server/app/tests/test_cases.json b/model_server/app/tests/test_cases.json
new file mode 100644
index 00000000..8fd7ec1e
--- /dev/null
+++ b/model_server/app/tests/test_cases.json
@@ -0,0 +1,794 @@
+[{
+   "case": "tool_call_halluciation",
+   "tokens" : ["<tool_call>"],
+   "expect": 1,
+   "logprobs": [[-0.3333307206630707,
+   -1.5310522317886353,
+   -3.5098977088928223,
+   -3.9004578590393066,
+   -5.775152683258057,
+   -5.814209461212158,
+   -5.9574151039123535,
+   -6.0094895362854,
+   -6.0094895362854,
+   -6.673445224761963]]
+},
+{
+   "case" : "parameter_value_hallucination",
+   "expect" : 0,
+   "tokens" : ["<tool_call>",
+   "\n",
+   "{'",
+   "name",
+   "':",
+   " '",
+   "get",
+   "_current",
+   "_weather",
+   "',",
+   " '",
+   "arguments",
+   "':",
+   " {'",
+   "location",
+   "':",
+   " '",
+   "Sea",
+   ",",
+   " Australia",
+   "',",
+   " '",
+   "unit",
+   "':",
+   " '",
+   "c",
+   "elsius",
+   "',",
+   " '",
+   "days",
+   "':",
+   " '",
+   "1",
+   "'}}\n",
+   "</tool_call>"],
+   "logprobs": [[-0.008103232830762863,
+   -5.085402488708496,
+   -6.777836799621582,
+   -7.558959007263184,
+   -9.850253105163574,
+   -10.266852378845215,
+   -10.540244102478027,
+   -10.722506523132324,
+   -10.800618171691895,
+   -10.917786598205566],
+  [0.0,
+   -23.25142478942871,
+   -25.139137268066406,
+   -26.2847843170166,
+   -28.992677688598633,
+   -29.070789337158203,
+   -29.55248260498047,
+   -29.91700553894043,
+   -30.20341682434082,
+   -30.307567596435547],
+  [0.0,
+   -21.66313934326172,
+   -23.06916046142578,
+   -23.32953453063965,
+   -25.65988540649414,
+   -25.985353469848633,
+   -26.519121170043945,
+   -27.07892417907715,
+   -27.977216720581055,
+   -28.458908081054688],
+  [0.0,
+   -28.094383239746094,
+   -28.56305694580078,
+   -29.109844207763672,
+   -29.44832992553711,
+   -31.79170036315918,
+   -32.0,
+   -32.05207443237305,
+   -32.31244659423828,
+   -32.364524841308594],
+  [0.0,
+   -30.489830017089844,
+   -31.140766143798828,
+   -31.81774139404297,
+   -34.525634765625,
+   -35.8275032043457,
+   -36.504478454589844,
+   -39.05614471435547,
+   -40.123680114746094,
+   -40.696502685546875],
+  [0.0,
+   -25.646865844726562,
+   -26.66232681274414,
+   -27.781936645507812,
+   -28.979660034179688,
+   -31.140764236450195,
+   -31.92188835144043,
+   -31.973962783813477,
+   -33.04149627685547,
+   -33.58828353881836],
+  [0.0,
+   -23.511798858642578,
+   -24.136695861816406,
+   -25.230268478393555,
+   -25.777053833007812,
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+   -26.45402717590332,
+   -26.636289596557617,
+   -26.740440368652344,
+   -26.896663665771484],
+  [0.0,
+   -22.366153717041016,
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+   -27.67778778076172,
+   -28.510986328125,
+   -28.615135192871094,
+   -29.13588523864746],
+  [0.0,
+   -22.52237319946289,
+   -24.292919158935547,
+   -24.344993591308594,
+   -24.39706802368164,
+   -24.73555564880371,
+   -29.943042755126953,
+   -29.969079971313477,
+   -30.021154403686523,
+   -30.0341739654541],
+  [0.0,
+   -30.17738151550293,
+   -30.411718368530273,
+   -30.88039207458496,
+   -30.984540939331055,
+   -31.270952224731445,
+   -31.895851135253906,
+   -32.46867370605469,
+   -32.624900817871094,
+   -33.484134674072266],
+  [0.0,
+   -28.146459579467773,
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+   -30.099267959594727,
+   -31.127744674682617,
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+   -32.807159423828125,
+   -33.7445068359375,
+   -33.770545959472656,
+   -34.069976806640625],
+  [0.0,
+   -26.323841094970703,
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+   -35.384864807128906,
+   -35.853538513183594],
+  [0.0,
+   -19.502033233642578,
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+  [0.0,
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+   -15.595710754394531,
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+   -18.121341705322266,
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+  [0.0,
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+   -26.037429809570312,
+   -26.115543365478516,
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+   -26.649309158325195],
+  [-0.03332124650478363,
+   -3.4181859493255615,
+   -15.759925842285156,
+   -15.812002182006836,
+   -16.593124389648438,
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+   -18.09027671813965,
+   -18.79328727722168,
+   -19.144792556762695,
+   -20.147233963012695],
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+   -22.7176570892334,
+   -24.13669776916504,
+   -24.188772201538086,
+   -24.34499740600586]]
+},
+{
+   "case": "fail_case",
+   "expect" : 0,
+   "tokens" : ["<tool_call>",
+   "\n",
+   "{'",
+   "name",
+   "':",
+   " '",
+   "get",
+   "_current",
+   "_weather",
+   "',",
+   " '",
+   "arguments",
+   "':",
+   " {'",
+   "location",
+   "':",
+   " '",
+   "Seattle",
+   ",",
+   " WA",
+   "',",
+   " '",
+   "unit",
+   "':",
+   " '",
+   "c",
+   "elsius",
+   "',",
+   " '",
+   "days",
+   "':",
+   " '",
+   "7",
+   "'}}\n",
+   "</tool_call>"],
+   "logprobs":[[-0.00013815402053296566,
+   -9.113236427307129,
+   -10.571331977844238,
+   -14.099404335021973,
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+  [-3.576278118089249e-07,
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+   -19.059398651123047,
+   -19.085433959960938],
+  [0.0,
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+   -18.903175354003906,
+   -20.829944610595703,
+   -22.574451446533203,
+   -22.860862731933594,
+   -23.069162368774414,
+   -23.32953643798828,
+   -23.694061279296875,
+   -24.188772201538086],
+  [0.0,
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+   -23.65500259399414,
+   -23.94141387939453,
+   -24.266881942749023]]
+}
+]
diff --git a/model_server/app/tests/test_hallucination.py b/model_server/app/tests/test_hallucination.py
new file mode 100644
index 00000000..25ad3303
--- /dev/null
+++ b/model_server/app/tests/test_hallucination.py
@@ -0,0 +1,60 @@
+import json
+from app.function_calling.hallucination_handler import HallucinationStateHandler
+import pytest
+import os
+
+# Get the directory of the current file
+current_dir = os.path.dirname(__file__)
+
+# Construct the full path to the JSON file
+json_file_path = os.path.join(current_dir, "test_cases.json")
+
+with open(json_file_path) as f:
+    test_cases = json.load(f)
+
+get_weather_api = {
+    "type": "function",
+    "function": {
+        "name": "get_current_weather",
+        "description": "Get current weather at a location.",
+        "parameters": {
+            "type": "object",
+            "properties": {
+                "location": {
+                    "type": "str",
+                    "description": "The location to get the weather for",
+                    "format": "City, State",
+                },
+                "unit": {
+                    "type": "str",
+                    "description": "The unit to return the weather in.",
+                    "enum": ["celsius", "fahrenheit"],
+                    "default": "celsius",
+                },
+                "days": {
+                    "type": "str",
+                    "description": "the number of days for the request.",
+                },
+            },
+            "required": ["location", "days"],
+        },
+    },
+}
+function_description = get_weather_api["function"]
+if type(function_description) != list:
+    function_description = [get_weather_api["function"]]
+
+
+@pytest.mark.parametrize("case", test_cases)
+def test_hallucination(case):
+    state = HallucinationStateHandler()
+    state.process_function(function_description)
+    for token, logprob in zip(case["tokens"], case["logprobs"]):
+        if token != "</tool_call>":
+            state.current_token = token
+            state.tokens.append(token)
+            state.logprobs.append(logprob)
+            state.process_token()
+            if state.hallucination:
+                break
+    assert state.hallucination == case["expect"]