diff --git a/Cargo.toml b/Cargo.toml
index 1dc28c4f..357d0cb3 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -106,3 +106,4 @@ bytes = "1.10.1"
 rand = "0.9.0"
 indoc = "2.0.6"
 owo-colors = "4.2.0"
+json5 = "0.4.1"
diff --git a/docs/docs/ai/llm.mdx b/docs/docs/ai/llm.mdx
index 02ced152..d4e751eb 100644
--- a/docs/docs/ai/llm.mdx
+++ b/docs/docs/ai/llm.mdx
@@ -97,4 +97,27 @@ cocoindex.LlmSpec(
 </TabItem>
 </Tabs>
 
-You can find the full list of models supported by Gemini [here](https://ai.google.dev/gemini-api/docs/models).
\ No newline at end of file
+You can find the full list of models supported by Gemini [here](https://ai.google.dev/gemini-api/docs/models).
+
+### Anthropic
+
+To use the Anthropic LLM API, you need to set the environment variable `ANTHROPIC_API_KEY`.
+You can generate the API key from [Anthropic API](https://console.anthropic.com/settings/keys).
+
+A spec for Anthropic looks like this:
+
+<Tabs>
+<TabItem value="python" label="Python" default>
+
+```python
+cocoindex.LlmSpec(
+    api_type=cocoindex.LlmApiType.ANTHROPIC,
+    model="claude-3-5-sonnet-latest",
+)
+```
+
+</TabItem>
+</Tabs>
+
+You can find the full list of models supported by Anthropic [here](https://docs.anthropic.com/en/docs/about-claude/models/all-models).
+
diff --git a/examples/manuals_llm_extraction/main.py b/examples/manuals_llm_extraction/main.py
index 2547c3fa..2115731f 100644
--- a/examples/manuals_llm_extraction/main.py
+++ b/examples/manuals_llm_extraction/main.py
@@ -98,6 +98,10 @@ def manual_extraction_flow(flow_builder: cocoindex.FlowBuilder, data_scope: coco
                 # Replace by this spec below, to use Gemini API model
                 #   llm_spec=cocoindex.LlmSpec(
                 #       api_type=cocoindex.LlmApiType.GEMINI, model="gemini-2.0-flash"),
+
+                # Replace by this spec below, to use Anthropic API model
+                #   llm_spec=cocoindex.LlmSpec(
+                #       api_type=cocoindex.LlmApiType.ANTHROPIC, model="claude-3-5-sonnet-latest"),
                 output_type=ModuleInfo,
                 instruction="Please extract Python module information from the manual."))
         doc["module_summary"] = doc["module_info"].transform(summarize_module)
diff --git a/python/cocoindex/llm.py b/python/cocoindex/llm.py
index 9db6da41..5fcd0a73 100644
--- a/python/cocoindex/llm.py
+++ b/python/cocoindex/llm.py
@@ -6,6 +6,7 @@ class LlmApiType(Enum):
     OPENAI = "OpenAi"
     OLLAMA = "Ollama"
     GEMINI = "Gemini"
+    ANTHROPIC = "Anthropic"
 
 @dataclass
 class LlmSpec:
diff --git a/src/llm/anthropic.rs b/src/llm/anthropic.rs
new file mode 100644
index 00000000..65cfcb49
--- /dev/null
+++ b/src/llm/anthropic.rs
@@ -0,0 +1,137 @@
+use async_trait::async_trait;
+use crate::llm::{LlmGenerationClient, LlmSpec, LlmGenerateRequest, LlmGenerateResponse, ToJsonSchemaOptions, OutputFormat};
+use anyhow::{Result, bail, Context};
+use serde_json::Value;
+use json5;
+
+use crate::api_bail;
+use urlencoding::encode;
+
+pub struct Client {
+    model: String,
+    api_key: String,
+    client: reqwest::Client,
+}
+
+impl Client {
+    pub async fn new(spec: LlmSpec) -> Result<Self> {
+        let api_key = match std::env::var("ANTHROPIC_API_KEY") {
+            Ok(val) => val,
+            Err(_) => api_bail!("ANTHROPIC_API_KEY environment variable must be set"),
+        };
+        Ok(Self {
+            model: spec.model,
+            api_key,
+            client: reqwest::Client::new(),
+        })
+    }
+}
+
+#[async_trait]
+impl LlmGenerationClient for Client {
+    async fn generate<'req>(
+        &self,
+        request: LlmGenerateRequest<'req>,
+    ) -> Result<LlmGenerateResponse> {
+        let messages = vec![serde_json::json!({
+            "role": "user",
+            "content": request.user_prompt
+        })];
+
+        let mut payload = serde_json::json!({
+            "model": self.model,
+            "messages": messages,
+            "max_tokens": 4096
+        });
+
+        // Add system prompt as top-level field if present (required)
+        if let Some(system) = request.system_prompt {
+            payload["system"] = serde_json::json!(system);
+        }
+
+        // Extract schema from output_format, error if not JsonSchema
+        let schema = match request.output_format.as_ref() {
+            Some(OutputFormat::JsonSchema { schema, .. }) => schema,
+            _ => api_bail!("Anthropic client expects OutputFormat::JsonSchema for all requests"),
+        };
+
+        let schema_json = serde_json::to_value(schema)?;
+        payload["tools"] = serde_json::json!([
+            { "type": "custom", "name": "report_result", "input_schema": schema_json }
+        ]);
+
+        let url = "https://api.anthropic.com/v1/messages";
+
+        let encoded_api_key = encode(&self.api_key);
+
+        let resp = self.client
+            .post(url)
+            .header("x-api-key", encoded_api_key.as_ref())
+            .header("anthropic-version", "2023-06-01")
+            .json(&payload)
+            .send()
+            .await
+            .context("HTTP error")?;
+        let mut resp_json: Value = resp.json().await.context("Invalid JSON")?;
+        if let Some(error) = resp_json.get("error") {
+            bail!("Anthropic API error: {:?}", error);
+        }
+
+        // Debug print full response
+        // println!("Anthropic API full response: {resp_json:?}");
+
+        let resp_content = &resp_json["content"];
+        let tool_name = "report_result"; 
+        let mut extracted_json: Option<Value> = None;
+        if let Some(array) = resp_content.as_array() {
+            for item in array {
+                if item.get("type") == Some(&Value::String("tool_use".to_string()))
+                    && item.get("name") == Some(&Value::String(tool_name.to_string()))
+                {
+                    if let Some(input) = item.get("input") {
+                        extracted_json = Some(input.clone());
+                        break;
+                    }
+                }
+            }
+        }
+        let text = if let Some(json) = extracted_json {
+            // Try strict JSON serialization first
+            serde_json::to_string(&json)?
+        } else {
+            // Fallback: try text if no tool output found
+            match &mut resp_json["content"][0]["text"] {
+                Value::String(s) => {
+                    // Try strict JSON parsing first
+                    match serde_json::from_str::<serde_json::Value>(s) {
+                        Ok(_) => std::mem::take(s),
+                        Err(e) => {
+                            // Try permissive json5 parsing as fallback
+                            match json5::from_str::<serde_json::Value>(s) {
+                                Ok(value) => {
+                                    println!("[Anthropic] Used permissive JSON5 parser for output");
+                                    serde_json::to_string(&value)?
+                                },
+                                Err(e2) => return Err(anyhow::anyhow!(format!("No structured tool output or text found in response, and permissive JSON5 parsing also failed: {e}; {e2}")))
+                            }
+                        }
+                    }
+                },
+                _ => return Err(anyhow::anyhow!("No structured tool output or text found in response")),
+            }
+        };
+
+        Ok(LlmGenerateResponse {
+            text,
+        })
+    }
+
+    fn json_schema_options(&self) -> ToJsonSchemaOptions {
+        ToJsonSchemaOptions {
+            fields_always_required: false,
+            supports_format: false,
+            extract_descriptions: false,
+            top_level_must_be_object: true,
+        }
+    }
+}
diff --git a/src/llm/mod.rs b/src/llm/mod.rs
index f06423d7..b91eed1c 100644
--- a/src/llm/mod.rs
+++ b/src/llm/mod.rs
@@ -12,6 +12,7 @@ pub enum LlmApiType {
     Ollama,
     OpenAi,
     Gemini,
+    Anthropic,
 }
 
 #[derive(Debug, Clone, Serialize, Deserialize)]
@@ -54,6 +55,7 @@ pub trait LlmGenerationClient: Send + Sync {
 mod ollama;
 mod openai;
 mod gemini;
+mod anthropic;
 
 pub async fn new_llm_generation_client(spec: LlmSpec) -> Result<Box<dyn LlmGenerationClient>> {
     let client = match spec.api_type {
@@ -66,6 +68,9 @@ pub async fn new_llm_generation_client(spec: LlmSpec) -> Result<Box<dyn LlmGener
         LlmApiType::Gemini => {
             Box::new(gemini::Client::new(spec).await?) as Box<dyn LlmGenerationClient>
         }
+        LlmApiType::Anthropic => {
+            Box::new(anthropic::Client::new(spec).await?) as Box<dyn LlmGenerationClient>
+        }
     };
     Ok(client)
 }