Large language models like GPT-4o and LLaMA are powering a new wave of AI applications, from chatbots and coding assistants to research tools. However, deploying these LLM-powered applications in production is far more challenging than traditional software or even typical machine learning systems.LLMs are massive and non-deterministic, often behaving as black boxes with unpredictable outputs. Issues such as false or biased answers can arise unexpectedly, and performance or cost can spiral if not managed. This is where LLM observability comes in.In this article, we will explain what LLM observability is and why it matters for managing LLM applications. We will explore common problems like hallucinations and prompt injection, distinguish observability from standard monitoring, and discuss the key challenges in debugging LLM systems. We will also highlight critical features to look for in LLM observability tools and survey the capabilities of current solutions. Finally, we will walk through a simple tutorial using W&B Weave to track an LLM’s outputs, detect anomalies such as hallucinations or bias, and visualize metrics. By the end, you will understand how LLM observability can enhance the reliability, performance, and trustworthiness of your LLM-driven applications. 

What is LLM observability?

 LLM observability refers to the tools, practices, and infrastructure that give you visibility into every aspect of an LLM application’s behavior – from its technical performance (like latency or errors) to the quality of the content it generates. In simpler terms, it means having the ability to monitor, trace, and analyze how your LLM system is functioning and why it produces the outputs that it does.Unlike basic monitoring that might only track system metrics, LLM observability goes deeper to evaluate whether the model’s outputs are useful, accurate, and safe. It creates a feedback loop where raw data from the model (prompts, responses, internal metrics) is turned into actionable insights for developers and ML engineers.This observability is crucial for several reasons:First, running LLMs in production demands continuous oversight due to their complexity and unpredictability. Proper observability ensures the model is producing clean, high-quality outputs and allows teams to catch issues like inaccuracies or offensive content early. It helps mitigate hallucinations (made-up facts) by flagging questionable answers, and it guards against prompt injection attacks or other misuse by monitoring inputs and outputs for anomalies.Observability is also key to managing performance – you can track response times, throughput, and resource usage in real time to prevent latency spikes or outages. It aids in cost management by monitoring token consumption and API usage, so you are not surprised by an exorbitant bill.Moreover, strong observability supports secure and ethical deployments: by detecting bias or privacy leaks in outputs, and by providing audit trails, it helps ensure the LLM is used in a compliant and trustworthy manner. In short, LLM observability gives you the confidence to operate LLM applications reliably at scale, knowing you can spot and fix problems before they harm the user experience or the business.

Common issues in LLM applications

Even advanced LLMs can exhibit a variety of issues when deployed. Below are some of the common problems that necessitate careful observability:

Many of these issues are interrelated – for example, a prompt injection could lead to a toxic or biased output (combining security and ethical problems), or a hallucination could go unnoticed if user feedback isn’t gathered. LLM observability directly targets these pain points by providing the visibility and tools needed to detect when they occur and understand their causes. Next, we will see how observability differs from standard monitoring in tackling such problems. 

LLM observability vs. LLM monitoring

 It’s important to clarify the distinction between LLM monitoring and LLM observability in the context of LLM applications. In traditional software operations, monitoring usually means keeping track of key metrics and system health indicators (CPU usage, error rates, throughput, etc.) and setting up alerts when things go out of bounds. Observability is a broader, deeper approach – it not only collects metrics but also logs, traces, and other data that allow you to explore and explain why something is happening in the system.For LLMs, the difference can be summarized as follows:

To illustrate, imagine a scenario: your LLM-backed chatbot suddenly gives an incorrect (hallucinated) answer to a factual question, and also the response took 5 seconds instead of the usual 1 second. Basic monitoring might alert you that the error rate is up or that latency is high. But with observability, you could trace that specific request: the trace might reveal that the chatbot made a call to a knowledge base (vector database) which returned irrelevant data, causing the LLM to hallucinate an answer and take longer while searching.By examining the trace and logs, you discover the root cause – maybe a vector search query failed to retrieve the right document due to an indexing issue. This level of insight comes from having an observability framework in place, not just monitoring counters. LLM monitoring is necessary but not sufficient: it tells you the metrics status, whereas LLM observability gives you the power to ask arbitrary questions about your system’s behavior and get answers. In the next sections, we will dive into the unique challenges that make observability crucial for LLMs and what features an observability solution should have to address them.

Challenges in observing LLM systems

Building observability for LLM applications is hard because these systems present unique challenges beyond those of traditional software or simpler ML models. Here are some key challenges that LLM observability aims to address:

In summary, the challenges of LLM observability stem from the fact that LLM applications are unlike traditional apps – they are stochastic, complex, lack fixed expected outputs, and push the limits of current infrastructure. Observability practices are evolving to meet these challenges, providing the needed visibility to ensure such AI systems remain performant, reliable, and trustworthy.

Key features to look for in LLM observability tools

Given the above challenges, what capabilities should an ideal LLM observability solution provide? Whether you are evaluating commercial platforms or building your own toolkit, look for the following critical features that address the needs of LLM-based systems:

To recap, LLM observability tools should provide comprehensive chain tracing, full-stack visibility, explainability and anomaly detection, easy integration with scale and security, and features for ongoing evaluation and debugging. Table 1 below summarizes some of the essential components and features that make up a robust LLM observability solution:

Feature/Component Description & Purpose
Tracing & Logging Capture each step in LLM pipelines (prompts, calls, tool uses) as a trace. Enables step-by-step debugging and performance profiling of chains or agents.
Metrics Monitoring Track key metrics like latency, throughput, token usage, error rates, and resource utilization in real-time. Provides the backbone for detecting performance issues and ensuring SLAs.
Output Evaluation Continuously evaluate the quality of LLM outputs using automated metrics (accuracy, relevance, etc.) or human feedback. Helps catch hallucinations, irrelevance, or drops in quality over time.
Prompt & Context Analysis Log and analyze prompts and retrieved context. Facilitates prompt engineering by revealing which prompts lead to good or bad outputs and whether retrieval (in RAG systems) is effective.
Anomaly & Bias Detection Automatically flag unusual patterns such as spikes in toxic language, biased responses, or abnormal output lengths. Ensures issues like bias or policy violations are caught early for mitigation.
Full-Stack Integration Instrument all components (model, databases, APIs, UI) and integrate with devops tools. Correlate model behavior with infrastructure events (e.g., DB timeouts), and fit into existing monitoring/alerting systems.
Security & Privacy Provide features like PII redaction in logs, secure data handling, and protection against prompt injections. Maintains user data privacy and model safety while observing the system.
Visualization & Filtering UI User-friendly dashboards to visualize metrics trends, traces, and evaluation results. Powerful filtering/query to inspect specific subsets of interactions for deeper analysis and debugging.

 Table 1: Key components and features of an LLM observability solution. Each component plays a role in ensuring you have insight into both the technical performance and the semantic output quality of your LLM application. 

Overview of the LLM observability tooling landscape

LLM observability is a new and rapidly evolving field, and a variety of tools and platforms have emerged to help teams implement the features discussed above. These range from specialized startups and open-source frameworks to extensions of traditional monitoring products. Without focusing on specific product names, we can categorize the types of LLM observability tools available and the common capabilities they offer:

Despite the variety, most LLM observability tools share a common set of capabilities aligned with the features we discussed earlier. They log prompts and outputs, track performance metrics (latency, token usage, errors), allow you to trace requests through chain/agent logic, and provide ways to assess output quality (either via automated metrics or manual review interfaces). They also tend to support integration with external data stores (like vector databases, for retrieving context) and will log the interactions with those stores for you (e.g., which documents were retrieved for a given query). In fact, observability for RAG (Retrieval-Augmented Generation) systems is a focus area: tools are adding features to monitor the retrieval step’s performance and relevance, because it’s so critical for factual accuracy. For instance, an observability dashboard might show the percentage of questions for which the retrieved context actually contained the correct answer – if that drops, you know your knowledge base or retriever might be at fault rather than the language model.It’s worth noting that because this field is fast-moving, new features are being added to tools frequently. As of 2025, many platforms are starting to incorporate AI-assisted analytics, such as using an LLM itself to summarize or explain trends in the observability data (e.g., “these cluster of outputs look like they might be hallucinations about topic X”). Tools are also improving at handling feedback loops – connecting user feedback directly into the observability reports and even enabling one-click fine-tuning or prompt adjustments when an issue is identified.In choosing an observability approach, consider factors like ease of integration (how quickly can you instrument your app?), scalability & cost (will it handle your traffic and how expensive is the data logging?), LLM-specific insights (does it have features beyond generic monitoring, like bias detection or chain visualization?), and team workflow fit (do your engineers and ML scientists find the UI and data useful?). Many teams start with a combination of open-source logging and custom scripts, then graduate to a more specialized platform as their usage grows. Regardless of the tool, implementing LLM observability is an iterative process – you’ll refine what you monitor and the alerts you set as you learn more about your application’s behavior in the wild. The encouraging news is that a range of frameworks and platforms now support LLM observability, and they continue to evolve as best practices emerge.Next, let’s put some of these ideas into practice. We will walk through a tutorial using W&B Weave, an open-source toolkit by Weights & Biases designed for LLM observability, to see how one can trace LLM calls, log outputs, and even detect issues like hallucinations in a simple application.

Tutorial: Tracking LLM outputs and anomalies with W&B Weave

In this section, we will demonstrate a simplified workflow for adding observability to an LLM application using W&B Weave. Weave is a toolkit that helps developers instrument and monitor LLM applications by capturing traces of function calls, logging model inputs/outputs, and evaluating those outputs with custom or built-in metrics.The scenario for our tutorial is a toy Q&A application: we have a function that calls an LLM to answer questions, and we want to track the behavior of this function over time, including detecting any hallucinated answers or biased content. We will use a synthetic setup (so you can follow along without needing a real API key, though Weave can integrate with real LLM APIs easily). The tutorial will cover:

  1. Setup and instrumentation: Installing W&B Weave and annotating our LLM call function to enable tracing.
  2. Logging LLM calls: Running the instrumented function to generate some example outputs and sending those logs to Weave.
  3. Anomaly detection with guardrails: Using Weave’s built-in Guardrails scorers to automatically evaluate outputs for issues like hallucinations or toxicity.
  4. Visualizing traces and metrics: Viewing the collected traces and metrics in the Weave UI to identify any anomalies.

   Let’s go step by step.

1. Install and initialize W&B Weave

First, install the weave library (it’s open-source and can be installed via pip) and log in to Weights & Biases with your API key (you can get a free key by creating a W&B account). In your environment, you would run:

pip install weave wandbwandb login # to authenticate with your W&B API key

For this tutorial, let’s assume we have done that. Now, in our Python code, we import weave and initialize a Weave project for our observability logs:

import weaveimport asynciofrom typing import Dict, Any# Initialize a Weave project (logs will go here)weave.init(“llm-observability-demo”)

Calling weave.init(“…”) sets up a project (replace with your chosen project name) and prepares Weave to start capturing data. You might be prompted to log in if not already authenticated. Once initialized, Weave will hook into any functions we decorate with @weave.op to trace their execution.

2. Instrument the LLM call with @weave.op

We have a function answer_question(prompt: str) -> str that uses an LLM to answer a given question. Normally, inside this function you would call your LLM API (e.g., OpenAI or a local model). For illustration, we will simulate an LLM response. We will also simulate that sometimes the “LLM” might hallucinate (we can do this by purposely returning an incorrect answer for certain inputs).Here’s how we instrument the function:

@weave.op() # This decorator tells Weave to track this function’s inputs/outputsdef answer_question(question: str) -> str: “””Call the LLM to get an answer to the question.””” # Simulate a response (for demo, we hard-code a couple of cases) if “capital of France” in question: return “The capital of France is Paris.” elif “president of France” in question: # Let’s simulate a hallucination here: return “The president of France is Napoleon Bonaparte.” # (Incorrect – hallucinated) else: # A default generic response return “I’m sorry, I don’t have the information on that.”

In a real scenario, inside answer_question you might use something like openai.Completion.create(…) or your model’s inference call. You would still decorate it with @weave.op() in the same way. The decorator ensures that whenever answer_question is called, Weave will log the call, including the input argument (question) and the returned result, along with execution time and any other metadata.We also included a docstring (which Weave can capture as well), and in our simulated logic we deliberately put a mistake: if asked “Who is the president of France?”, our fake LLM returns “Napoleon Bonaparte” – clearly a hallucination or error (Napoleon is long dead and not a president). This will help demonstrate how we catch such issues.Now, let’s call our function a few times to generate some data:

questions = [ “What is the capital of France?”, “Who is the president of France?”, “How many legs does a spider have?”]for q in questions: answer = answer_question(q) # calling the op (this gets logged by Weave) print(f”Q: {q}nA: {answer}n”)

When you run this loop, a few things happen:

  After running the above, your console might show something like: Each call to answer_question is considered a traced run, which you can inspect.

3. Adding guardrails for output evaluation

Now that we have basic logging, let’s introduce Weave’s Guardrails feature to evaluate the outputs. W&B Weave Guardrails provides pre-built scorers that automatically check LLM inputs or outputs for issues like toxicity, bias, or hallucination. We will use a hallucination detection scorer for our example.Weave’s scorers can be used in two modes:

 For observability, we will use monitor mode to log whether our outputs are likely hallucinated. Under the hood, a hallucination scorer might compare the LLM’s answer with the provided context or use a separate model to fact-check the answer.Here’s how we might integrate a scorer in code (simplified):

# Create a custom scorer for hallucination detectionclass HallucinationScorer(weave.Scorer): @weave.op def score(self, output: str) -> dict: “””A simple hallucination detector that flags certain keywords.””” # A dummy check: flag as hallucination if certain keyword is in output. # In practice, this could call a model or check against a knowledge base. hallucinated = “Napoleon” in output # just for demo criteria return { “hallucination”: 1 if hallucinated else 0, “confidence”: 0.9 if hallucinated else 0.1 } # Create a dataset of our questions for evaluationdataset = [ {“question”: “What is the capital of France?”}, {“question”: “Who is the president of France?”}, {“question”: “How many legs does a spider have?”}] # Create an evaluationevaluation = weave.Evaluation( dataset=dataset, scorers=[HallucinationScorer()]) # Run the evaluationresults = evaluation.evaluate(answer_question)print(“Evaluation complete! Check the Weave UI for detailed results.”)

Let’s break that down:

  When the scorer runs, Weave will log the scorer’s output just like any other op. Since we’ve attached it to the original call, Weave knows this is an evaluation of that call. Now, in the Weave UI, every recorded call of answer_question will have an associated hallucination score. If our dummy logic is correct, the call for “Who is the president of France?” will have hallucination: 1 (meaning flagged) while the others have 0.We could similarly add other scorers – for example, a toxicity scorer to check if the output contains hate speech (not likely in our simple Q&A, but useful in general), or a relevancy scorer to check if the answer stayed on topic. Weave provides several built-in scorers that you can use out of the box, and you can easily create custom ones like we did above.Here’s an example with multiple scorers:

# Additional scorer for answer relevancyclass RelevancyScorer(weave.Scorer): @weave.op def score(self, question: str, output: str) -> dict: “””Check if the answer is relevant to the question.””” if “don’t have the information” in output: return {“relevancy”: 0.2} # Low relevancy for non-answers elif any(word in output.lower() for word in question.lower().split()): return {“relevancy”: 0.8} # High relevancy if answer contains question words else: return {“relevancy”: 0.5} # Medium relevancy otherwise # Update our evaluation with multiple scorersevaluation = weave.Evaluation( dataset=dataset, scorers=[HallucinationScorer(), RelevancyScorer()]) # Run the evaluation with multiple metricsresults = evaluation.evaluate(answer_question)

Which we can analyze in Weave: The key idea is that we are augmenting each LLM output with evaluation metrics. These metrics become part of our observability data – they can be visualized and aggregated. Weave’s evaluation framework essentially allows every LLM call to be automatically analyzed for quality and safety issues, and since all data is logged, we can later review how often hallucinations happened or if any outputs were flagged for bias. 

4. Visualizing traces and metrics in Weave

With data now logged (our prompt, response, and a hallucination flag), we head to the Weights & Biases interface to examine it. When you open the project in your browser, you will see a list of runs or traces. Each call to answer_question is recorded as an interactive trace.Key features you’ll find in the Weave UI:

  1. Traces Tab: Shows all your function calls with inputs, outputs, and timing information
  2. Evaluation Results: When you run evaluations, you’ll see aggregated results and can drill down into individual scored calls
  3. Call Details: Click on any call to see full details including the evaluation scores attached to that specific call

  In the trace details, you can see:

    Crucially, because we ran an evaluation, the traces will show the evaluation results. For the “president of France” question, you would see something like:

  While the other questions would show:

 Weave provides tools to filter and chart these metrics. You can create dashboards showing hallucination frequency over time, compare different model versions, and set up alerts if certain thresholds are exceeded.Advanced Analysis Features:

   

Summary

This tutorial demonstrates a basic but complete observability workflow using W&B Weave:

  1. Instrumentation: We decorated our LLM function with @weave.op() for automatic tracing
  2. Logging: Every function call is automatically logged with inputs, outputs, and metadata
  3. Evaluation: We created custom scorers to detect hallucinations and assess relevancy
  4. Analysis: All data flows to the Weave UI where you can analyze patterns, set up alerts, and track model quality over time

   Key takeaways:

   This is a basic example, but you can imagine scaling this up. In a production app with W&B Weave, you might trace entire user conversations (with each message as a trace span), log context retrieved from a vector database, and attach multiple evaluation checks (for factuality, bias, security). The result is a rich dataset that you can use to constantly improve your LLM system.Observability helps you iterate faster: you notice an issue (e.g., a pattern of mistakes), you fix something (change prompt or model), and then use the observability data to confirm the issue is resolved and no new ones have appeared.

LLM observability metrics and evaluation

Throughout this article, we’ve mentioned various metrics and evaluation criteria for LLM performance. Let’s bring those into focus and answer some key questions about how we assess LLM outputs and system performance. Broadly, there are two kinds of metrics to consider when we talk about LLM observability:

 Both types are crucial to LLM observability, as they address the two fundamental aspects: making sure the model is saying the right things (quality) and doing so efficiently and safely (performance).

Quality evaluation metrics for LLM outputs

Measuring the quality of LLM outputs is challenging because it’s often subjective and context-dependent. However, there are several evaluation metrics and methods that can be used as proxies to quantify aspects of output quality. Here are some important ones:

  Other quality metrics include accuracy (especially for QA tasks – whether the content is factually correct), coherence/fluency (does the text read well and logically?), and specificity (is the answer sufficiently specific vs. vague). Often, a composite of metrics or a custom scoring function is used. For example, you might define a scorecard for an answer that combines relevance, correctness, and clarity.Here’s a summary table of the key quality metrics discussed:

Metric What it Measures Why It Matters
Relevance How well the LLM’s output addresses the user’s query or intended task. High relevance means the answer is on-topic and useful for the question. Ensures the model is actually solving the user’s problem. Irrelevant answers indicate misunderstanding or evasive behavior, which hurts user trust and experience.
Perplexity A measure of the model’s confidence/predictability on a given text (lower is better). Essentially, how “surprised” the model is by the content it produces or encounters. Tracks the model’s overall language proficiency and can flag distribution shifts. A spike in perplexity might mean inputs are out-of-distribution or the model is struggling to generate likely text, often correlating with confusion or errors in output.
Fairness/Bias Quantifies biases or unfair behavior in outputs, often by comparing responses across different demographic or sensitive contexts (or via toxicity/bias classifiers). Maintains ethical standards and prevents harm. Monitoring bias metrics ensures the model’s outputs do not systematically favor or disfavor any group, and helps catch toxic or discriminatory language early.

 Table 1: Example quality-focused metrics for evaluating LLM outputs. In practice, these metrics may be computed via automated tools or human annotation, and no single metric tells the whole story – but together they provide a multi-dimensional view of output quality. 

System performance and resource metrics for LLMs

Alongside output quality, observability must track operational metrics that reflect the performance and efficiency of the LLM application. These metrics are similar to those in traditional web services, but with some LLM-specific twists. Here are key observability metrics on the system side and their impact:

   To compile these into a visual summary:

System Metric Definition Impact on Performance & Utilization
Latency Time taken to produce a response to a request (often measured in milliseconds or seconds). High latency harms user experience and indicates bottlenecks. Monitoring latency (avg and tail) helps ensure the app stays responsive and helps identify slow components causing delays.
Throughput Processing capacity of the system (e.g., requests per second or tokens per second it can handle). Affects scalability and cost-efficiency. Throughput metrics reveal how the system performs under load – low throughput at scale means potential backlogs and need for optimization or more resources.
Token Usage & Cost Number of input/output tokens per request, and aggregate tokens (often converted to monetary cost for API-based models). Helps manage and predict costs. Spikes in token usage may signal longer outputs (possible model drift or verbose hallucinations) and can significantly increase latency and cost if unchecked. Observing this helps optimize prompts and responses for brevity and relevance.
Resource Utilization CPU/GPU utilization, memory usage, and other hardware metrics while running the LLM workload. Ensures system is operating within safe limits. High utilization suggests bottlenecks or need to scale out. For example, sustained 100% GPU can maximize performance but risk slowdowns if load increases further, whereas low utilization means you have headroom or over-provisioned resources.
Error Rate Frequency of errors/failures in handling requests (e.g., exceptions, timeouts, content filter triggers). A rising error rate directly impacts reliability and user trust. Monitoring errors allows quick detection of problems like service outages, bugs, or unacceptable content filters. Keeping error rate low (and quickly addressing spikes) is key to robust service.

 Table 2: Key performance and resource metrics for LLM applications. By tracking these, teams can ensure the system remains efficient and stable under real-world usage.With the combination of quality metrics (like relevance, correctness, fairness) and system metrics (like latency, throughput, usage), LLM observability provides a holistic view of an application’s health. You can tell not only “Is the system up and running within limits?” but also “Is it delivering the expected quality of output to users?”.

Conclusion

As we have explored, LLM observability is an essential discipline for anyone deploying large language model applications in the real world. It extends beyond traditional monitoring by giving us deep insights into both the performance and the behavior of our AI systems. By implementing observability for LLMs, teams can ensure their applications produce accurate, relevant, and safe outputs, while also running efficiently and reliably. This means we can catch hallucinations before they mislead users, mitigate prompt injection attacks or data leaks, reduce latency and cost issues, and maintain oversight of ethical considerations like bias and fairness. In a sense, observability is our compass for navigating the inherently unpredictable landscape of generative AI – it helps turn the black box of an LLM into a glass box, where we can see what’s going on and steer it in the right direction.In practice, building LLM observability involves capturing a rich set of telemetry: prompts, responses, intermediate steps, metrics, logs, and feedback. We then need tools to aggregate and analyze this data, from dashboards that plot key metrics to automated alerts and evaluations that flag anomalies. Thankfully, the tooling ecosystem is rising to the challenge. As we discussed, numerous frameworks (open-source and commercial) are available to help implement observability. Whether you use a specialized platform or assemble your own with open libraries, the important thing is to establish that feedback loop: observe -> diagnose -> improve -> repeat. For instance, using a tool like W&B Weave can jumpstart this process by instrumenting your application with minimal code changes and providing immediate visualization of how your model is performing. Our tutorial showed a glimpse of how easy it can be to log every LLM call and even attach evaluations for things like hallucinations or bias. With such setups, ML engineers and stakeholders can confidently track the quality of their LLMs over time and across versions.The benefits of incorporating LLM observability are clear. Teams gain faster debugging and iteration – instead of guessing why an AI behaved a certain way, they can pinpoint it in the logs or trace. They achieve better model performance and user satisfaction by continuously monitoring and refining prompts, models, and system parameters based on real data. Observability also provides a safety net for responsible AI, catching harmful outputs and enabling audits (critical for compliance and trust). Moreover, it helps with cost control and scaling, as you have detailed usage metrics to inform infrastructure decisions.As you develop and deploy LLM-powered applications, treat observability as a first-class concern, not an afterthought. Start with the question: “How will we know if our model is doing the right thing and doing it well?” and let that guide your observability design. By implementing the strategies and features outlined in this article – from tracing LLM chains to monitoring key metrics and using evaluation tools – you will empower your team to manage LLM applications proactively and effectively. The era of large language models is full of opportunities, but also uncertainties; with robust observability, we turn those uncertainties into actionable knowledge.If you’re ready to enhance your LLM application’s observability, consider exploring tools like W&B Weave. They can save you time and provide advanced capabilities out-of-the-box for tracing, evaluating, and improving your LLM. By investing in observability, you’re investing in the long-term success and scalability of your AI application.