This commit is contained in:
Ishaan Jaffer
2026-01-24 12:09:16 -08:00
parent a081dc2ee2
commit bbeb007f4e
2 changed files with 279 additions and 145 deletions
@@ -2,42 +2,45 @@
Tool search enables Claude to dynamically discover and load tools on-demand from large tool catalogs (10,000+ tools). Instead of loading all tool definitions into the context window upfront, Claude searches your tool catalog and loads only the tools it needs.
## Supported Providers
| Provider | Chat Completions API | Messages API |
|----------|---------------------|--------------|
| **Anthropic API** | ✅ | ✅ |
| **Azure Anthropic** (Microsoft Foundry) | ✅ | ✅ |
| **Google Cloud Vertex AI** | ✅ | ✅ |
| **Amazon Bedrock** | ✅ (Invoke API only, Opus 4.5 only) | ✅ (Invoke API only, Opus 4.5 only) |
## Benefits
- **Context efficiency**: Avoid consuming massive portions of your context window with tool definitions
- **Better tool selection**: Claude's tool selection accuracy degrades with more than 30-50 tools. Tool search maintains accuracy even with thousands of tools
- **On-demand loading**: Tools are only loaded when Claude needs them
## Supported Models
Tool search is available on:
- Claude Opus 4.5
- Claude Sonnet 4.5
## Supported Platforms
- Anthropic API (direct)
- Azure Anthropic (Microsoft Foundry)
- Google Cloud Vertex AI
- Amazon Bedrock (invoke API only, not converse API)
## Tool Search Variants
LiteLLM supports both tool search variants:
### 1. Regex Tool Search (`tool_search_tool_regex_20251119`)
Claude constructs regex patterns to search for tools.
Claude constructs regex patterns to search for tools. Best for exact pattern matching (faster).
### 2. BM25 Tool Search (`tool_search_tool_bm25_20251119`)
Claude uses natural language queries to search for tools using the BM25 algorithm.
Claude uses natural language queries to search for tools using the BM25 algorithm. Best for natural language semantic search.
## Quick Start
**Note**: BM25 variant is not supported on Bedrock.
### Basic Example with Regex Tool Search
---
```python
## Chat Completions API
### SDK Usage
#### Basic Example with Regex Tool Search
```python showLineNumbers title="Basic Tool Search Example"
import litellm
response = litellm.completion(
@@ -70,26 +73,6 @@ response = litellm.completion(
}
},
"defer_loading": True # Mark for deferred loading
},
# Another deferred tool
{
"type": "function",
"function": {
"name": "search_files",
"description": "Search through files in the workspace",
"parameters": {
"type": "object",
"properties": {
"query": {"type": "string"},
"file_types": {
"type": "array",
"items": {"type": "string"}
}
},
"required": ["query"]
}
},
"defer_loading": True
}
]
)
@@ -97,9 +80,9 @@ response = litellm.completion(
print(response.choices[0].message.content)
```
### BM25 Tool Search Example
#### BM25 Tool Search Example
```python
```python showLineNumbers title="BM25 Tool Search"
import litellm
response = litellm.completion(
@@ -134,9 +117,9 @@ response = litellm.completion(
)
```
## Using with Azure Anthropic
#### Azure Anthropic Example
```python
```python showLineNumbers title="Azure Anthropic Tool Search"
import litellm
response = litellm.completion(
@@ -170,9 +153,9 @@ response = litellm.completion(
)
```
## Using with Vertex AI
#### Vertex AI Example
```python
```python showLineNumbers title="Vertex AI Tool Search"
import litellm
response = litellm.completion(
@@ -192,11 +175,9 @@ response = litellm.completion(
)
```
## Streaming Support
#### Streaming Support
Tool search works with streaming:
```python
```python showLineNumbers title="Streaming with Tool Search"
import litellm
response = litellm.completion(
@@ -233,13 +214,13 @@ for chunk in response:
print(chunk.choices[0].delta.content, end="")
```
## LiteLLM Proxy
### AI Gateway Usage
Tool search works automatically through the LiteLLM proxy:
Tool search works automatically through the LiteLLM proxy.
### Proxy Config
#### Proxy Configuration
```yaml
```yaml showLineNumbers title="config.yaml"
model_list:
- model_name: claude-sonnet
litellm_params:
@@ -247,9 +228,9 @@ model_list:
api_key: os.environ/ANTHROPIC_API_KEY
```
### Client Request
#### Client Request
```python
```python showLineNumbers title="Client Request via Proxy"
import openai
client = openai.OpenAI(
@@ -286,127 +267,279 @@ response = client.chat.completions.create(
)
```
## Important Notes
---
### Beta Header
## Messages API
LiteLLM automatically detects tool search tools and adds the appropriate beta header based on your provider:
The Messages API provides native Anthropic-style tool search support via the `litellm.anthropic.messages` interface.
- **Anthropic API & Microsoft Foundry**: `advanced-tool-use-2025-11-20`
- **Google Cloud Vertex AI**: `tool-search-tool-2025-10-19`
- **Amazon Bedrock** (Invoke API, Opus 4.5 only): `tool-search-tool-2025-10-19`
### SDK Usage
You don't need to manually specify beta headers—LiteLLM handles this automatically.
#### Basic Example
### Deferred Loading
```python showLineNumbers title="Messages API - Basic Tool Search"
import litellm
- Tools with `defer_loading: true` are only loaded when Claude discovers them via search
- At least one tool must be non-deferred (the tool search tool itself)
- Keep your 3-5 most frequently used tools as non-deferred for optimal performance
### Tool Descriptions
Write clear, descriptive tool names and descriptions that match how users describe tasks. The search algorithm uses:
- Tool names
- Tool descriptions
- Argument names
- Argument descriptions
### Usage Tracking
Tool search requests are tracked in the usage object:
```python
response = litellm.completion(
model="anthropic/claude-sonnet-4-5-20250929",
messages=[{"role": "user", "content": "Search for tools"}],
tools=[...]
response = await litellm.anthropic.messages.acreate(
model="anthropic/claude-sonnet-4-20250514",
messages=[
{
"role": "user",
"content": "What's the weather in San Francisco?"
}
],
tools=[
{
"type": "tool_search_tool_regex_20251119",
"name": "tool_search_tool_regex"
},
{
"name": "get_weather",
"description": "Get the current weather for a location",
"input_schema": {
"type": "object",
"properties": {
"location": {
"type": "string",
"description": "The city and state, e.g. San Francisco, CA"
}
},
"required": ["location"]
},
"defer_loading": True
}
],
max_tokens=1024,
extra_headers={"anthropic-beta": "advanced-tool-use-2025-11-20"}
)
# Check tool search usage
if response.usage.server_tool_use:
print(f"Tool search requests: {response.usage.server_tool_use.tool_search_requests}")
print(response)
```
## Error Handling
#### Azure Anthropic Messages Example
### All Tools Deferred
```python showLineNumbers title="Azure Anthropic Messages API"
import litellm
```python
# ❌ This will fail - at least one tool must be non-deferred
tools = [
{
"type": "function",
"function": {...},
"defer_loading": True
}
]
# ✅ Correct - tool search tool is non-deferred
tools = [
{
"type": "tool_search_tool_regex_20251119",
"name": "tool_search_tool_regex"
},
{
"type": "function",
"function": {...},
"defer_loading": True
}
]
response = await litellm.anthropic.messages.acreate(
model="azure_anthropic/claude-sonnet-4-20250514",
messages=[
{
"role": "user",
"content": "What's the stock price of Apple?"
}
],
tools=[
{
"type": "tool_search_tool_regex_20251119",
"name": "tool_search_tool_regex"
},
{
"name": "get_stock_price",
"description": "Get the current stock price for a ticker symbol",
"input_schema": {
"type": "object",
"properties": {
"ticker": {
"type": "string",
"description": "The stock ticker symbol, e.g. AAPL"
}
},
"required": ["ticker"]
},
"defer_loading": True
}
],
max_tokens=1024,
extra_headers={"anthropic-beta": "advanced-tool-use-2025-11-20"}
)
```
### Missing Tool Definition
#### Vertex AI Messages Example
If Claude references a tool that isn't in your deferred tools list, you'll get an error. Make sure all tools that might be discovered are included in the tools parameter with `defer_loading: true`.
```python showLineNumbers title="Vertex AI Messages API"
import litellm
## Best Practices
response = await litellm.anthropic.messages.acreate(
model="vertex_ai/claude-sonnet-4@20250514",
messages=[
{
"role": "user",
"content": "Search the web for information about AI"
}
],
tools=[
{
"type": "tool_search_tool_bm25_20251119",
"name": "tool_search_tool_bm25"
},
{
"name": "search_web",
"description": "Search the web for information",
"input_schema": {
"type": "object",
"properties": {
"query": {
"type": "string",
"description": "The search query"
}
},
"required": ["query"]
},
"defer_loading": True
}
],
max_tokens=1024,
extra_headers={"anthropic-beta": "tool-search-tool-2025-10-19"}
)
```
1. **Keep frequently used tools non-deferred**: Your 3-5 most common tools should not have `defer_loading: true`
#### Bedrock Messages Example
2. **Use semantic descriptions**: Tool descriptions should use natural language that matches user queries
```python showLineNumbers title="Bedrock Messages API (Invoke)"
import litellm
3. **Choose the right variant**:
- Use **regex** for exact pattern matching (faster)
- Use **BM25** for natural language semantic search
response = await litellm.anthropic.messages.acreate(
model="bedrock/invoke/anthropic.claude-opus-4-20250514-v1:0",
messages=[
{
"role": "user",
"content": "What's the weather?"
}
],
tools=[
{
"type": "tool_search_tool_regex_20251119",
"name": "tool_search_tool_regex"
},
{
"name": "get_weather",
"description": "Get weather information",
"input_schema": {
"type": "object",
"properties": {
"location": {"type": "string"}
},
"required": ["location"]
},
"defer_loading": True
}
],
max_tokens=1024,
extra_headers={"anthropic-beta": "tool-search-tool-2025-10-19"}
)
```
4. **Monitor usage**: Track `tool_search_requests` in the usage object to understand search patterns
#### Streaming Support
5. **Optimize tool catalog**: Remove unused tools and consolidate similar functionality
```python showLineNumbers title="Messages API - Streaming"
import litellm
import json
## When to Use Tool Search
response = await litellm.anthropic.messages.acreate(
model="anthropic/claude-sonnet-4-20250514",
messages=[
{
"role": "user",
"content": "What's the weather in Tokyo?"
}
],
tools=[
{
"type": "tool_search_tool_regex_20251119",
"name": "tool_search_tool_regex"
},
{
"name": "get_weather",
"description": "Get weather information",
"input_schema": {
"type": "object",
"properties": {
"location": {"type": "string"}
},
"required": ["location"]
},
"defer_loading": True
}
],
max_tokens=1024,
stream=True,
extra_headers={"anthropic-beta": "advanced-tool-use-2025-11-20"}
)
**Good use cases:**
- 10+ tools available in your system
- Tool definitions consuming >10K tokens
- Experiencing tool selection accuracy issues
- Building systems with multiple tool categories
- Tool library growing over time
async for chunk in response:
if isinstance(chunk, bytes):
chunk_str = chunk.decode("utf-8")
for line in chunk_str.split("\n"):
if line.startswith("data: "):
try:
json_data = json.loads(line[6:])
print(json_data)
except json.JSONDecodeError:
pass
```
**When traditional tool calling is better:**
- Less than 10 tools total
- All tools are frequently used
- Very small tool definitions (\<100 tokens total)
### AI Gateway Usage
## Limitations
Configure the proxy to use Messages API endpoints.
- Not compatible with tool use examples
- Requires Claude Opus 4.5 or Sonnet 4.5
- On Bedrock, only available via invoke API (not converse API)
- On Bedrock, only supported for Claude Opus 4.5 (not Sonnet 4.5)
- BM25 variant (`tool_search_tool_bm25_20251119`) is not supported on Bedrock
- Maximum 10,000 tools in catalog
- Returns 3-5 most relevant tools per search
#### Proxy Configuration
### Bedrock-Specific Notes
```yaml showLineNumbers title="config.yaml"
model_list:
- model_name: claude-sonnet-messages
litellm_params:
model: anthropic/claude-sonnet-4-20250514
api_key: os.environ/ANTHROPIC_API_KEY
```
When using Bedrock's Invoke API:
- The regex variant (`tool_search_tool_regex_20251119`) is automatically normalized to `tool_search_tool_regex`
- The BM25 variant (`tool_search_tool_bm25_20251119`) is automatically filtered out as it's not supported
- Tool search is only available for Claude Opus 4.5 models
#### Client Request
```python showLineNumbers title="Client Request via Proxy (Messages API)"
import httpx
async with httpx.AsyncClient() as client:
response = await client.post(
"http://0.0.0.0:4000/anthropic/v1/messages",
headers={
"Authorization": "Bearer your-litellm-proxy-key",
"anthropic-beta": "advanced-tool-use-2025-11-20"
},
json={
"model": "claude-sonnet-messages",
"messages": [
{
"role": "user",
"content": "What's the weather?"
}
],
"tools": [
{
"type": "tool_search_tool_regex_20251119",
"name": "tool_search_tool_regex"
},
{
"name": "get_weather",
"description": "Get weather information",
"input_schema": {
"type": "object",
"properties": {
"location": {"type": "string"}
},
"required": ["location"]
},
"defer_loading": True
}
],
"max_tokens": 1024
}
)
print(response.json())
```
---
## Additional Resources
- [Anthropic Tool Search Documentation](https://docs.anthropic.com/en/docs/build-with-claude/tool-use/tool-search)
- [LiteLLM Tool Calling Guide](https://docs.litellm.ai/docs/completion/function_call)
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@@ -843,6 +843,7 @@ const sidebars = {
"completion/image_generation_chat",
"completion/json_mode",
"completion/knowledgebase",
"providers/anthropic_tool_search",
"guides/code_interpreter",
"completion/message_trimming",
"completion/model_alias",