strands.vended_plugins.context_injector.plugin

ContextInjector plugin for injecting just-in-time context into the model input.

This module provides the ContextInjector plugin, which folds just-in-time text into the model input before each call without touching durable history.

Example:

import datetime

from strands import Agent
from strands.vended_plugins.context_injector import ContextInjector

agent = Agent(
    plugins=[
        ContextInjector(lambda context: f"<now>\{datetime.datetime.now().isoformat()}</now>")
    ]
)

ContextInjector

class ContextInjector(Plugin)

Defined in: src/strands/vended_plugins/context_injector/plugin.py:37

Plugin that injects just-in-time context into the model input before each call.

Before each model call, the plugin asks render_content for text and makes it available to the model for that call, gated by trigger. The injected text is ephemeral: it augments the model input for that one call and never persists into the durable conversation or session.

Multiple injectors may be registered; each contributes its text independently, in plugin-registration order.

Arguments:

render_content - Renders the text to inject for this call, or None/"" to skip. Sync or async. The text reaches the model verbatim, so it is a prompt-injection
surface - escape any attacker-influenced fields yourself. A callback that raises fails open (injection is skipped, the model call proceeds).
name - Plugin name, for logging and duplicate detection. Defaults to "strands:context-injector". Set a distinct name when registering more than one injector so they can be told apart.
trigger - When to inject. An InjectionTrigger name selects a built-in policy ("userTurn" — default — or "everyTurn"); a predicate over the InjectionContext is the escape hatch. A predicate that raises fails open (injection is skipped). Defaults to "userTurn".

Example:

from strands import Agent
from strands.vended_plugins.context_injector import ContextInjector

agent = Agent(
    plugins=[
        ContextInjector(lambda context: f"<context>\{derive(context.messages)}</context>")
    ]
)

init

def __init__(render_content: RenderContent,
             *,
             name: str | None = None,
             trigger: InjectionTriggerPredicate | None = None) -> None

Defined in: src/strands/vended_plugins/context_injector/plugin.py:76

Initialize the ContextInjector plugin.

Arguments:

render_content - Renders the text to inject for this call. Sync or async.
name - Plugin name. Defaults to "strands:context-injector".
trigger - When to inject. Defaults to "userTurn".

init_agent

def init_agent(agent: Agent) -> None

Defined in: src/strands/vended_plugins/context_injector/plugin.py:95