Implementation:Truera Trulens TruApp Wrapper

Knowledge Sources	TruLens TruLens Custom App Guide
Domains	Observability, LLM_Evaluation
Last Updated	2026-02-14 08:00 GMT

Overview

Concrete tool for wrapping arbitrary Python classes with @instrument-decorated methods for tracing and evaluation, provided by the trulens-core library.

Description

The TruApp class is the most flexible recorder in TruLens. It wraps any Python class instance whose methods are decorated with @instrument. TruApp discovers instrumented methods, identifies the main entry point, and provides context manager recording.

TruApp automatically discovers methods decorated with the RECORD_ROOT span type to use as the main method. If no RECORD_ROOT method is found, a main method can be specified explicitly.

Usage

Import and use TruApp when your application is a custom Python class (not a LangChain chain or LangGraph graph). First decorate methods with @instrument, then wrap with TruApp.

Code Reference

Source Location

• Repository: trulens
• File: src/core/trulens/apps/app.py
• Lines: L218-499

Signature

class TruApp(core_app.App):
    app: Any

    def __init__(
        self,
        app: Any,
        main_method: Optional[Callable] = None,
        methods_to_instrument=None,
        **kwargs: Any,
    ):
        """
        Args:
            app: Any Python class instance to instrument.
            main_method: Optional entry point method. Auto-detected from
                RECORD_ROOT-decorated methods if not specified.
            methods_to_instrument: Optional dict of additional methods to
                instrument.
            **kwargs: Additional arguments including:
                app_name (str): Application name.
                app_version (str): Version tag.
                feedbacks (List[Feedback]): Feedback functions.
                connector (DBConnector): Optional database connector.
        """

Import

from trulens.apps.app import TruApp

I/O Contract

Inputs

Name	Type	Required	Description
app	Any	Yes	Python class instance with @instrument-decorated methods
main_method	Callable	No	Entry point method (auto-detected if RECORD_ROOT decorated)
app_name	str	No	Application name (via kwargs)
app_version	str	No	Version tag (via kwargs)
feedbacks	List[Feedback]	No	Feedback functions for evaluation (via kwargs)

Outputs

Name	Type	Description
return	TruApp	Instrumented wrapper supporting context manager recording

Usage Examples

Custom RAG App

from trulens.core.otel.instrument import instrument
from trulens.otel.semconv.trace import SpanAttributes
from trulens.apps.app import TruApp

class MyRAG:
    @instrument(span_type=SpanAttributes.SpanType.RETRIEVAL)
    def retrieve(self, query: str) -> list:
        return self.vector_store.query(query)

    @instrument(span_type=SpanAttributes.SpanType.GENERATION)
    def generate(self, context: str, query: str) -> str:
        return self.llm.invoke(f"{context}\n{query}")

    @instrument()
    def respond(self, query: str) -> str:
        contexts = self.retrieve(query)
        return self.generate("\n".join(contexts), query)

my_app = MyRAG()

tru_recorder = TruApp(
    my_app,
    main_method=my_app.respond,
    app_name="Custom_RAG",
    app_version="v1",
    feedbacks=[f_relevance, f_groundedness],
)

with tru_recorder as recording:
    result = my_app.respond("What is TruLens?")

Related Pages

Implements Principle

• Principle:Truera_Trulens_Custom_App_Wrapping

Requires Environment

• Environment:Truera_Trulens_Python_Core_Environment