MiddlewareAgent¶
MiddlewareAgent wraps a pydantic-ai AbstractAgent and applies middleware hooks
around its run() and iter() methods. It is the main entry point for using
middleware with any pydantic-ai agent.
Key responsibilities:
- Applies
before_runhooks (in order) before the agent processes a prompt. - Wraps all toolsets with
MiddlewareToolsetsobefore_tool_call,after_tool_call, andon_tool_errorhooks intercept every tool invocation. - Applies
after_runhooks (in reverse order) after the agent completes. - Applies
on_errorhooks when an exception occurs. - Stores run metadata (usage, prompts, outputs) in the
MiddlewareContextwhen provided.
pydantic_ai_middleware.MiddlewareAgent
¶
Bases: AbstractAgent[AgentDepsT, OutputDataT]
Agent that wraps another agent and applies middleware hooks.
Middleware is applied in order for before_* hooks and in reverse order for after_* hooks, similar to ASGI/WSGI middleware.
Source code in src/pydantic_ai_middleware/agent.py
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|---|---|
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wrapped
property
¶
The wrapped agent.
middleware
property
¶
The middleware list.
__init__(agent, middleware=None, context=None, permission_handler=None)
¶
Initialize the middleware agent.
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
agent
|
AbstractAgent[AgentDepsT, OutputDataT]
|
The agent to wrap. |
required |
middleware
|
list[AgentMiddleware[AgentDepsT]] | None
|
List of middleware to apply. |
None
|
context
|
MiddlewareContext | None
|
MiddlewareContext instance for sharing data between hooks. If not provided, context features are disabled. |
None
|
permission_handler
|
PermissionHandler | None
|
Callback for handling ASK permission decisions from before_tool_call. Called with (tool_name, tool_args, reason) and should return True to allow or False to deny. |
None
|
Source code in src/pydantic_ai_middleware/agent.py
run(user_prompt=None, *, output_type=None, message_history=None, deferred_tool_results=None, model=None, instructions=None, deps=None, model_settings=None, usage_limits=None, usage=None, metadata=None, infer_name=True, toolsets=None, builtin_tools=None, event_stream_handler=None)
async
¶
Run the agent with middleware hooks applied.
Parameters:
| Name | Type | Description | Default |
|---|---|---|---|
user_prompt
|
str | Sequence[UserContent] | None
|
User input to start/continue the conversation. |
None
|
output_type
|
OutputSpec[Any] | None
|
Custom output type for this run. |
None
|
message_history
|
Sequence[ModelMessage] | None
|
History of the conversation so far. |
None
|
deferred_tool_results
|
DeferredToolResults | None
|
Results for deferred tool calls. |
None
|
model
|
Model | KnownModelName | str | None
|
Optional model to use for this run. |
None
|
instructions
|
Instructions[AgentDepsT]
|
Optional additional instructions. |
None
|
deps
|
AgentDepsT
|
Optional dependencies for this run. |
None
|
model_settings
|
ModelSettings | None
|
Optional settings for the model request. |
None
|
usage_limits
|
UsageLimits | None
|
Optional limits on model requests or tokens. |
None
|
usage
|
RunUsage | None
|
Optional usage to start with. |
None
|
metadata
|
AgentMetadata[AgentDepsT] | None
|
Optional metadata for the agent run. |
None
|
infer_name
|
bool
|
Whether to infer agent name from call frame. |
True
|
toolsets
|
Sequence[AbstractToolset[AgentDepsT]] | None
|
Optional additional toolsets for this run. |
None
|
builtin_tools
|
Sequence[AbstractBuiltinTool | BuiltinToolFunc[AgentDepsT]] | None
|
Optional additional builtin tools. |
None
|
event_stream_handler
|
EventStreamHandler[AgentDepsT] | None
|
Optional handler for stream events. |
None
|
Returns:
| Type | Description |
|---|---|
AgentRunResult[Any]
|
The result of the agent run. |
Source code in src/pydantic_ai_middleware/agent.py
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iter(user_prompt=None, *, output_type=None, message_history=None, deferred_tool_results=None, model=None, instructions=None, deps=None, model_settings=None, usage_limits=None, usage=None, metadata=None, infer_name=True, toolsets=None, builtin_tools=None)
async
¶
Iterate over agent execution with middleware applied.
Source code in src/pydantic_ai_middleware/agent.py
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override(**kwargs)
¶
Context manager to temporarily override agent settings.
Accepts the same keyword arguments as the wrapped agent's override method (name, deps, model, toolsets, tools, instructions).