Use this guide when you want to optimize **tool signatures** (descriptions + parameter descriptions) separately from prompt text or agent logic.

## What this covers

- Optimize MCP tool descriptions without touching prompt content.
- Keep system/assistant/user messages fixed while improving tool calling behavior.
- Target only specific tools when a server exposes many tools.

:::callout{intent="note" title="Separate from prompt or agent optimization"}
Tool optimization updates tool signatures. Prompt optimization updates system/user/assistant content.
Agent optimization focuses on multi-step agent logic. Keep these runs separate to isolate changes.
:::

## Quickstart: tool-only optimization

```python
from opik_optimizer import ChatPrompt, MetaPromptOptimizer

prompt = ChatPrompt(
    system="Use tools when needed.",
    user="{user_query}",
    tools=[
        {
            "type": "mcp",
            "server_label": "context7",
            "server_url": "https://mcp.context7.com/mcp",
            "allowed_tools": ["resolve-library-id", "query-docs"],
        }
    ],
)

optimizer = MetaPromptOptimizer(model="openai/gpt-4o-mini")
result = optimizer.optimize_prompt(
    prompt=prompt,
    dataset=my_dataset,
    metric=answer_quality,
    optimize_prompts=False,  # keep prompt text fixed
    optimize_tools=True,     # optimize tool + parameter descriptions
)
```

Tool optimization is supported by all optimizers **except** `FewShotBayesianOptimizer`,
`ParameterOptimizer`, and `GepaOptimizer` (for now).

## Tool calling + MCP formats

You can define tools in one of the supported formats. Tool optimization will normalize them to
function-calling tools while preserving the original MCP config for reproducibility.

### Supported formats

| Format                         | When to use                             | Example                                                                         |
| ------------------------------ | --------------------------------------- | ------------------------------------------------------------------------------- |
| OpenAI MCP tool entry (local)  | Run MCP tool servers locally            | `{"type": "mcp", "server_label": "...", "command": "...", "args": [...]}`       |
| OpenAI MCP tool entry (remote) | Call remote MCP servers                 | `{"type": "mcp", "server_label": "...", "server_url": "...", "headers": {...}}` |
| Cursor MCP config              | Convert from a Cursor `mcpServers` JSON | `cursor_mcp_config_to_tools(cursor_config)`                                     |
| Function tools                 | Non-MCP tools in OpenAI function format | `{"type": "function", "function": {...}}`                                       |

### OpenAI MCP tool entries (local/remote)

```python
prompt = ChatPrompt(
    system="Use tools when needed.",
    user="{user_query}",
    tools=[
        {
            "type": "mcp",
            "server_label": "local_docs",
            "command": "npx",
            "args": ["-y", "@upstash/context7-mcp"],
            "env": {},
            "allowed_tools": ["resolve-library-id", "query-docs"],
        },
        {
            "type": "mcp",
            "server_label": "remote_docs",
            "server_url": "https://mcp.context7.com/mcp",
            "headers": {"CONTEXT7_API_KEY": "YOUR_API_KEY"},
            "allowed_tools": ["query-docs"],
        },
    ],
)
```

### Cursor MCP config (JSON) → tools

```python
from opik_optimizer.utils.toolcalling import cursor_mcp_config_to_tools

cursor_config = {
    "mcpServers": {
        "context7": {
            "url": "https://mcp.context7.com/mcp",
            "headers": {"CONTEXT7_API_KEY": "YOUR_API_KEY"},
        }
    }
}

prompt = ChatPrompt(
    system="Use tools when needed.",
    user="{user_query}",
    tools=cursor_mcp_config_to_tools(cursor_config),
)
```

### Cursor vs OpenAI ChatPrompt styles

`ChatPrompt.tools` accepts OpenAI-style MCP entries directly. Cursor configs use a different
shape (`mcpServers`) and must be converted first:

```python
# OpenAI-style MCP tool entry (directly supported by ChatPrompt.tools)
openai_tools = [
    {
        "type": "mcp",
        "server_label": "context7",
        "server_url": "https://mcp.context7.com/mcp",
        "headers": {"CONTEXT7_API_KEY": "YOUR_API_KEY"},
        "allowed_tools": ["resolve-library-id", "query-docs"],
    }
]

# Cursor-style config (convert before assigning to ChatPrompt.tools)
cursor_config = {
    "mcpServers": {
        "context7": {
            "url": "https://mcp.context7.com/mcp",
            "headers": {"CONTEXT7_API_KEY": "YOUR_API_KEY"},
        }
    }
}
```

After normalization, both styles execute the same way during evaluation and optimization.

### Mixed function + MCP tools

```python
prompt = ChatPrompt(
    system="Use tools when needed.",
    user="{user_query}",
    tools=[
        {
            "type": "function",
            "function": {
                "name": "search_wikipedia",
                "description": "Search Wikipedia abstracts.",
                "parameters": {
                    "type": "object",
                    "properties": {"query": {"type": "string"}},
                    "required": ["query"],
                },
            },
        },
        {
            "type": "mcp",
            "server_label": "context7",
            "server_url": "https://mcp.context7.com/mcp",
            "allowed_tools": ["query-docs"],
        },
    ],
)
```

## Target only specific tools

When a server exposes many tools, pass a dict to select the subset you want:

```python
result = optimizer.optimize_prompt(
    prompt=prompt,
    dataset=my_dataset,
    metric=answer_quality,
    optimize_prompts=False,
    optimize_tools={
        "context7.resolve-library-id": True,
        "context7.query-docs": False,
    },
)
```

## Tool optimization limits

To keep runs manageable, `optimize_tools=True` is limited by
`DEFAULT_TOOL_CALL_MAX_TOOLS_TO_OPTIMIZE` (default: 3). If you need more, pass a dict
to select a smaller subset of tools.

## Disable tool use while optimizing tools

If you want to optimize tool descriptions without executing tools during evaluation, set
`allow_tool_use=False`:

```python
result = optimizer.optimize_prompt(
    prompt=prompt,
    dataset=my_dataset,
    metric=answer_quality,
    optimize_prompts=False,
    optimize_tools=True,
    allow_tool_use=False,  # do not execute tools during evaluation
)
```

## What changes

- Tool **descriptions** are updated.
- Tool **parameter descriptions** are updated.
- Prompt text stays unchanged when `optimize_prompts=False`.

:::accordion{title="Where the optimized tool signature is stored"}
The optimized tools are returned in `result.prompt.tools`. History entries include both the resolved tools and the original MCP config for reproducibility.
:::

## When to use tool optimization

| Scenario                                  | Use tool optimization? | Why                                                   |
| ----------------------------------------- | ---------------------- | ----------------------------------------------------- |
| MCP client injects assistant instructions | Yes                    | Keep assistant text fixed and improve tool usage.     |
| Prompt wording needs improvement          | No                     | Use `optimize_prompts` instead.                       |
| Multi-agent workflows                     | Maybe                  | Optimize tools separately before agent-level changes. |

## Limitations

- Tool optimization only supports **single prompts**.
- Not supported in `FewShotBayesianOptimizer`, `ParameterOptimizer`, or `GepaOptimizer`.

## Troubleshooting

### See tool-calling debug logs

Set the optimizer log level to surface tool calls:

```bash
export OPIK_OPTIMIZER_LOG_LEVEL=DEBUG
```

You’ll see tool call lines like:

```
tool: event=tool_call call=query-docs({...})
```

### I get “MCP remote server missing url”

Make sure your tool entry includes `server_url` (OpenAI MCP format) or `url` (Cursor config).

### Tools are not showing up

- Verify the MCP server is reachable.
- If using `allowed_tools`, confirm the names match the server’s tool list.
- For remote servers, confirm auth headers are correct.

### Tool calls are slow or failing during evaluation

- Set `allow_tool_use=False` to optimize descriptions without running tools.
- Reduce dataset size while iterating on tool descriptions.

## Next steps

- [Optimize prompts](https://www.comet.com/development/optimization-runs/optimization/optimize_prompts)
- [Optimize agents](https://www.comet.com/development/optimization-runs/optimization/optimize_agents)
- [Tool optimization algorithm](https://www.comet.com/development/optimization-runs/algorithms/tool_optimization)

## Related pages

- [Opik Agent Optimizer Core Concepts](./development-optimization-runs-optimization-concepts.md)
- [Configuring LLM Providers](./development-optimization-runs-optimization-configure-models.md)
- [Define datasets](./development-optimization-runs-optimization-define-datasets.md)
- [Define metrics](./development-optimization-runs-optimization-define-metrics.md)
- [Optimize prompts](./development-optimization-runs-optimization-optimize-prompts.md)
- [Optimize agents](./development-optimization-runs-optimization-optimize-agents.md)
- [Optimize multimodal prompts](./development-optimization-runs-optimization-optimize-multimodal.md)
- [Dashboard results](./development-optimization-runs-optimization-dashboard-results.md)

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