Customize traces

You can customize how you trace to better understand how your application runs and make it easier to find and fix problems. By adjusting how you collect and manage trace data, you can better track complex processes, monitor systems that work across multiple services, and debug issues more effectively.

Annotating your code

You can add traces for multiple, specific functions in your code to your logs by annotating them with functional wrappers (TypeScript) or decorators and context managers (Python):

import { initLogger, wrapOpenAI, wrapTraced } from "braintrust";
import OpenAI from "openai";
import { ChatCompletionMessageParam } from "openai/resources";
 
const logger = initLogger({
  projectName: "My Project",
  apiKey: process.env.BRAINTRUST_API_KEY,
});
 
const client = wrapOpenAI(
  new OpenAI({
    apiKey: process.env.OPENAI_API_KEY,
  }),
);
 
// wrapTraced() automatically logs the input (args) and output (return value)
// of this function to a span. To ensure the span is named `answerQuestion`,
// you should name the inline function definition (inside of wrapTraced).
const answerQuestion = wrapTraced(async function answerQuestion(
  body: string,
): Promise<string> {
  const prompt: ChatCompletionMessageParam[] = [
    { role: "system", content: "You are a helpful assistant." },
    { role: "user", content: body },
  ];
 
  const result = await client.chat.completions.create({
    model: "gpt-4o",
    messages: prompt,
  });
 
  const content = result.choices[0].message.content;
  if (!content) {
    throw new Error("The LLM response content is empty or undefined.");
  }
 
  return content;
});
 
async function main() {
  const input = "How can I improve my productivity?";
  const result = await answerQuestion(input);
  console.log(result);
}

Wrapping LLM clients

Wrapping OpenAI

When using wrapOpenAI/wrap_openai, you technically do not need to use traced or start_span. In fact, just initializing a logger is enough to start logging LLM calls. If you use traced or start_span, you will create more detailed traces that include the functions surrounding the LLM calls and can group multiple LLM calls together.

Streaming metrics

wrap_openai/wrapOpenAI will automatically log metrics like prompt_tokens, completion_tokens, and total_tokens for streaming LLM calls if the LLM API returns them. OpenAI only returns these metrics if you set include_usage to true in the stream_options parameter.

import { OpenAI } from "openai";
import { initLogger, traced, wrapOpenAI, wrapTraced } from "braintrust";
 
const client = wrapOpenAI(new OpenAI());
const logger = initLogger({
  projectName: "My Project",
  apiKey: process.env.BRAINTRUST_API_KEY,
});
 
async function main() {
  const result = await client.chat.completions.create({
    model: "gpt-4o",
    messages: [{ role: "user", content: "What is 1+1?" }],
    stream: true,
    stream_options: {
      include_usage: true,
    },
  });
 
  for await (const chunk of result) {
    console.log(chunk);
  }
}
 
main().catch(console.error);

Wrapping a custom LLM client

If you're using your own client, you can wrap it yourself using the same conventions as the OpenAI wrapper. Feel free to check out the Python and TypeScript implementations for reference.

To track the span as an LLM, you must:

• Specify the type as llm. You can specify any name you'd like. This enables LLM duration metrics.
• Add prompt_tokens, completion_tokens, and total_tokens to the metrics field. This enables LLM token usage metrics.
• Format the input as a list of messages (using the OpenAI format), and put other parameters (like model) in metadata. This enables the "Try prompt" button in the UI.

import { initLogger, traced, wrapTraced } from "braintrust";
 
const logger = initLogger({
  projectName: "My Project",
  apiKey: process.env.BRAINTRUST_API_KEY,
});
 
interface LLMCompletion {
  completion: string;
  metrics: {
    prompt_tokens: number;
    completion_tokens: number;
  };
}
 
async function callMyLLM(
  input: string,
  params: { temperature: number },
): Promise<LLMCompletion> {
  // Replace with your custom LLM implementation
  return {
    completion: "Hello, world!",
    metrics: {
      prompt_tokens: input.length,
      completion_tokens: 10,
    },
  };
}
 
export const invokeCustomLLM = wrapTraced(
  async function invokeCustomLLM(
    llmInput: string,
    params: { temperature: number },
  ) {
    return traced(async (span) => {
      const result = await callMyLLM(llmInput, params);
      const content = result.completion;
      span.log({
        input: [{ role: "user", content: llmInput }],
        output: content,
        metrics: {
          prompt_tokens: result.metrics.prompt_tokens,
          completion_tokens: result.metrics.completion_tokens,
          total_tokens:
            result.metrics.prompt_tokens + result.metrics.completion_tokens,
        },
        metadata: params,
      });
      return content;
    });
  },
  {
    type: "llm",
    name: "Custom LLM",
  },
);
 
export async function POST(req: Request) {
  return traced(async (span) => {
    const result = await invokeCustomLLM(await req.text(), {
      temperature: 0.1,
    });
    span.log({ input: req.body, output: result });
    return result;
  });
}

Multimodal content

Uploading attachments

In addition to text and structured data, Braintrust also supports uploading file attachments (blobs). This is especially useful when working with multimodal models, which can require logging large image, audio, or video files. You can also use attachments to log other unstructured data related to your LLM usage, such as a user-provided PDF file that your application later transforms into an LLM input.

To upload an attachment, create a new Attachment object to represent the file on disk or binary data in memory to be uploaded. You can place Attachment objects anywhere in the event to be logged, including in arrays/lists or deeply nested in objects. See the TypeScript or Python SDK reference for usage details.

import { Attachment, initLogger } from "braintrust";
 
const logger = initLogger({ projectName: "Attachment Example" });
 
logger.log({
  input: {
    question: "What is this?",
    context: new Attachment({
      data: "path/to/input_image.jpg",
      filename: "user_input.jpg",
      contentType: "image/jpeg",
    }),
  },
  output: "Example response.",
});

The SDK uploads the attachments separately from other parts of the log, so the presence of attachments doesn't affect non-attachment logging latency.

Image, audio, video, and PDF attachments can be previewed in Braintrust. All attachments can be downloaded for viewing locally.

Linking to external images

To log an external image, provide an image URL or base64 encoded image as a string. The tree viewer will automatically render the image.

The tree viewer will look at the URL or string to determine if it is an image. If you want to force the viewer to treat it as an image, then nest it in an object like

{
  "image_url": {
    "url": "https://example.com/image.jpg"
  }
}

and the viewer will render it as an image. Base64 images must be rendered in URL format, just like the OpenAI API. For example:

data:image/png;base64,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

Errors

When you run:

• Python code inside of the @traced decorator or within a start_span() context
• TypeScript code inside of traced (or a wrappedTraced function)

Braintrust will automatically log any exceptions that occur within the span.

Under the hood, every span has an error field which you can also log to directly.

import { wrapTraced, currentSpan } from "braintrust";
 
async function processRequest(input: string) {
  return input.length > 10
    ? { error: "Input too long" }
    : { data: "Hello, world!" };
}
 
const requestHandler = wrapTraced(async function requestHandler(req: Request) {
  const body = await req.text();
  const result = await processRequest(body);
  if (result.error) {
    currentSpan().log({ error: result.error });
  } else {
    currentSpan().log({ input: req.body, output: result.data });
  }
  return result;
});

Deeply nested code

Often, you want to trace functions that are deep in the call stack, without having to propagate the span object throughout. Braintrust uses async-friendly context variables to make this workflow easy:

• The traced function/decorator will create a span underneath the currently-active span.
• The currentSpan() / current_span() method returns the currently active span, in case you need to do additional logging.

import {
  currentSpan,
  initLogger,
  traced,
  wrapOpenAI,
  wrapTraced,
} from "braintrust";
import OpenAI from "openai";
 
const logger = initLogger();
const client = wrapOpenAI(
  new OpenAI({
    apiKey: process.env.OPENAI_API_KEY,
  }),
);
 
export const runLLM = wrapTraced(async function runLLM(input) {
  const model = Math.random() > 0.5 ? "gpt-4o" : "gpt-4o-mini";
  const result = await client.chat.completions.create({
    model,
    messages: [{ role: "user", content: input }],
  });
  const output = result.choices[0].message.content;
  currentSpan().log({
    metadata: {
      randomModel: model,
    },
  });
  return output;
});
 
export const someLogic = wrapTraced(async function someLogic(input: string) {
  return await runLLM(
    "You are a magical wizard. Answer the following question: " + input,
  );
});
 
export async function POST(req: Request) {
  return await traced(async () => {
    const body = await req.json();
    const result = await someLogic(body.text);
    currentSpan().log({
      input: body.text,
      output: result,
      metadata: { user_id: body.userId },
    });
    return result;
  });
}

Distributed tracing

Sometimes it's useful to be able to start a trace in one process and continue it in a different one. For this purpose, Braintrust provides an export function which returns an opaque string identifier. This identifier can be passed to start_span to resume the trace elsewhere. Consider the following example of tracing across separate client and server processes.

Client code

import { currentSpan, initLogger, wrapTraced } from "braintrust";
import { ChatCompletionMessageParam } from "openai/resources";
 
const logger = initLogger({ projectName: "my-project" });
 
async function remoteChatCompletion(args: {
  model: string;
  messages: ChatCompletionMessageParam[];
  extraHeaders?: Record<string, string>;
}) {
  // This is a placeholder for code that would call a remote service
}
 
const bedTimeStory = wrapTraced(async function bedtimeStory(input: {
  summary: string;
  length: number;
}) {
  return await remoteChatCompletion({
    model: "gpt-3.5-turbo",
    messages: [
      {
        role: "system",
        content:
          "Come up with a bedtime story with the following summary and approximate length (in words)",
      },
      {
        role: "user",
        content: `summary: ${input.summary}\nlength: ${input.length}`,
      },
    ],
    extraHeaders: {
      request_id: await currentSpan().export(),
    },
  });
});

Server code

import { traced, wrapOpenAI } from "braintrust";
import OpenAI from "openai";
import { ChatCompletionMessageParam } from "openai/resources";
 
const client = wrapOpenAI(
  new OpenAI({
    apiKey: process.env.OPENAI_API_KEY,
  }),
);
 
async function serverSideChatCompletion(request: {
  model: string;
  messages: ChatCompletionMessageParam[];
  headers?: Record<string, string>;
}) {
  return await traced(
    async (span) => {
      const output = await client.chat.completions.create({
        model: request.model,
        messages: request.messages,
      });
      return output.choices[0].message.content;
    },
    {
      name: "text_generator_server",
      type: "llm",
      // This will be a fresh, root-level trace if headers or request_id are undefined,
      // or will create sub-spans under the parent trace if they are defined.
      parent: request.headers?.request_id,
    },
  );
}

Updating spans

Similar to distributed tracing, it can be useful to update spans after you initially log them. For example, if you collect the output of a span asynchronously.

The Experiment and Logger classes each have an updateSpan() method, which you can call with the span's id to perform an update:

import { initLogger, wrapTraced, currentSpan } from "braintrust";
 
const logger = initLogger({
  projectName: "my-project", // Replace with your project name
  apiKey: process.env.BRAINTRUST_API_KEY, // Replace with your API key
});
 
const startRequest = wrapTraced(async function startRequest(request) {
  const handle = startSomething(request.body);
  return {
    result: handle,
    spanId: currentSpan().id,
  };
});
 
const finishRequest = wrapTraced(async function finishRequest(handle, spanId) {
  const result = await finishSomething(handle);
  logger.updateSpan({
    id: spanId,
    output: result,
  });
  return result;
});

You can also use span.export() to export the span in a fully contained string, which is useful if you have multiple loggers or perform the update from a different service.

import { initLogger, wrapTraced, currentSpan, updateSpan } from "braintrust";
 
const logger = initLogger({
  projectName: "my-project", // Replace with your project name
  apiKey: process.env.BRAINTRUST_API_KEY, // Replace with your API key
});
 
const startRequest = wrapTraced(async function startRequest(request) {
  const handle = startSomething(request.body);
  return {
    result: handle,
    exported: currentSpan().export(),
  };
});
 
const finishRequest = wrapTraced(
  async function finishRequest(handle, exported) {
    const result = await finishSomething(handle);
    updateSpan({
      exported,
      output: result,
    });
    return result;
  },
);

Deep-linking to spans

The Span.permalink method formats a permalink to the Braintrust application for viewing the span. The link will open the UI to the row represented by the Span object.

If you do not have access to the original Span object, the slug produced by Span.export contains enough information to produce the same permalink. The braintrust.permalink function can be used to construct a deep link to the row in the UI from a given span slug.

Manually managing spans

In more complicated environments, it may not always be possible to wrap the entire duration of a span within a single block of code. In such cases, you can always pass spans around manually.

Consider this hypothetical server handler, which logs to a span incrementally over several distinct callbacks:

import {
  Span,
  initLogger,
  startSpan,
  wrapOpenAI,
  wrapTraced,
} from "braintrust";
import { OpenAI } from "openai";
 
const client = wrapOpenAI(new OpenAI({ apiKey: process.env.OPENAI_API_KEY }));
const logger = initLogger({ projectName: "My long-running project" });
 
const computeOutput = wrapTraced(async function computeOutput(
  systemPrompt: string,
  userInput: string,
  parentSpan: Span,
) {
  return await client.chat.completions.create({
    model: "gpt-3.5-turbo",
    messages: [
      { role: "system", content: systemPrompt },
      { role: "user", content: userInput },
    ],
  });
});
 
class MyHandler {
  private liveSpans: Record<string, { span: Span; input: string }>;
 
  constructor() {
    this.liveSpans = {};
  }
 
  async onRequestStart(requestId: string, input: string, expected: string) {
    const span = startSpan({ name: requestId, event: { input, expected } });
    this.liveSpans[requestId] = { span, input };
  }
 
  async onGetOutput(requestId: string, systemPrompt: string) {
    const { span, input } = this.liveSpans[requestId];
    const output = await computeOutput(systemPrompt, input, span);
    span.log({ output });
  }
 
  async onRequestEnd(requestId: string, metadata: Record<string, string>) {
    const { span } = this.liveSpans[requestId];
    delete this.liveSpans[requestId];
    span.log({ metadata });
    span.end();
  }
}

Importing and exporting spans

Spans are processed in Braintrust as a simple format, consisting of input, output, expected, metadata, scores, and metrics fields (all optional), as well as a few system-defined fields which you usually do not need to mess with, but are described below for completeness. This simple format makes it easy to import spans captured in other systems (e.g. languages other than TypeScript/Python), or to export spans from Braintrust to consume in other systems.

Underlying format

The underlying span format contains a number of fields which are not exposed directly through the SDK, but are useful to understand when importing/exporting spans.

• id is a unique identifier for the span, within the container (e.g. an experiment, or logs for a project). You can technically set this field yourself (to overwrite a span), but it is recommended to let Braintrust generate it automatically.
• input, output, expected, scores, metadata, and metrics are optional fields which describe the span and are exposed in the Braintrust UI. When you use the TypeScript or Python SDK, these fields are validated for you (e.g. scores must be a mapping from strings to numbers between 0 and 1).
• span_attributes contains attributes about the span. Currently the recognized attributes are name, which is used to display the span name in the UI, and type, which displays a helpful icon. type should be one of "llm", "score", "function", "eval", "task", or "tool".
• Depending on the container, e.g. an experiment, or project logs, or a dataset, fields like project_id, experiment_id, dataset_id, and log_id are set automatically, by the SDK, so the span can be later retrieved by the UI and API. You should not set these fields yourself.
• span_id, root_span_id, and span_parents are used to construct the span tree and are automatically set by Braintrust. You should not set these fields yourself, but rather let the SDK create and manage them (even if importing from another system).

When importing spans, the only fields you should need to think about are input, output, expected, scores, metadata, and metrics. You can use the SDK to populate the remaining fields, which the next section covers with an example.

Here is an example of a span in the underlying format:

{
  "id": "385052b6-50a2-43b4-b52d-9afaa34f0bff",
  "input": {
    "question": "What is the origin of the customer support issue??"
  },
  "output": {
    "answer": "The customer support issue originated from a bug in the code.",
    "sources": ["http://www.example.com/faq/1234"]
  },
  "expected": {
    "answer": "Bug in the code that involved dividing by zero.",
    "sources": ["http://www.example.com/faq/1234"]
  },
  "scores": {
    "Factuality": 0.6
  },
  "metadata": {
    "pos": 1
  },
  "metrics": {
    "end": 1704872988.726753,
    "start": 1704872988.725727
    // Can also include `tokens`, etc. here
  },
  "project_id": "d709efc0-ac9f-410d-8387-345e1e5074dc",
  "experiment_id": "51047341-2cea-4a8a-a0ad-3000f4a94a96",
  "created": "2024-01-10T07:49:48.725731+00:00",
  "span_id": "70b04fd2-0177-47a9-a70b-e32ca43db131",
  "root_span_id": "68b4ef73-f898-4756-b806-3bdd2d1cf3a1",
  "span_parents": ["68b4ef73-f898-4756-b806-3bdd2d1cf3a1"],
  "span_attributes": {
    "name": "doc_included"
  }
}

Example import/export

The following example walks through how to generate spans in one program and then import them to Braintrust in a script. You can use this pattern to support tracing or running experiments in environments that use programming languages other than TypeScript/Python (e.g. Kotlin, Java, Go, Ruby, Rust, C++), or codebases that cannot integrate the Braintrust SDK directly.

Generating spans

The following example runs a simple LLM app and collects logging information at each stage of the process, without using the Braintrust SDK. This could be implemented in any programming language, and you certainly do not need to collect or process information this way. All that matters is that your program generates a useful format that you can later parse and use to import the spans using the SDK.

import json
import time
 
import openai
 
client = openai.OpenAI()
 
 
def run_llm(input, **params):
    start = time.time()
    messages = [{"role": "user", "content": input}]
    result = client.chat.completions.create(
        model="gpt-3.5-turbo", messages=[{"role": "user", "content": input}], **params
    )
    end = time.time()
    return {
        "input": messages,
        "output": result.choices[0].message.dict(),
        "metadata": {"model": "gpt-3.5-turbo", "params": params},
        "metrics": {
            "start": start,
            "end": end,
            "tokens": result.usage.total_tokens,
            "prompt_tokens": result.usage.prompt_tokens,
            "completion_tokens": result.usage.completion_tokens,
        },
        "name": "OpenAI Chat Completion",
    }
 
 
PROMPT_TEMPLATE = "Answer the following question: %s"
 
 
def run_input(question, expected):
    result = run_llm(PROMPT_TEMPLATE % question, max_tokens=32)
    return {
        "input": question,
        "output": result["output"]["content"],
        # Expected is propagated here to make it easy to use it in the import
        # script, but it's not strictly needed to be here.
        "expected": expected,
        "metadata": {
            "template": PROMPT_TEMPLATE,
        },
        "children": [result],
        "name": "run_input",
    }
 
 
if __name__ == "__main__":
    for question, expected in [
        [
            "What is 1+1?",
            "2.",
        ],
        [
            "Which is larger, the sun or the moon?",
            "The sun.",
        ],
    ]:
        print(json.dumps(run_input(question, expected)))

Running this script produces output like:

{"input": "What is 1+1?", "output": "The sum of 1+1 is 2.", "expected": "2.", "metadata": {"template": "Answer the following question: %s"}, "children": [{"input": [{"role": "user", "content": "Answer the following question: What is 1+1?"}], "output": {"content": "The sum of 1+1 is 2.", "role": "assistant", "function_call": null, "tool_calls": null}, "metadata": {"model": "gpt-3.5-turbo", "params": {"max_tokens": 32}}, "metrics": {"start": 1704916642.978631, "end": 1704916643.450115, "tokens": 30, "prompt_tokens": 19, "completion_tokens": 11}, "name": "OpenAI Chat Completion"}], "name": "run_input"}
{"input": "Which is larger, the sun or the moon?", "output": "The sun is larger than the moon.", "expected": "The sun.", "metadata": {"template": "Answer the following question: %s"}, "children": [{"input": [{"role": "user", "content": "Answer the following question: Which is larger, the sun or the moon?"}], "output": {"content": "The sun is larger than the moon.", "role": "assistant", "function_call": null, "tool_calls": null}, "metadata": {"model": "gpt-3.5-turbo", "params": {"max_tokens": 32}}, "metrics": {"start": 1704916643.450675, "end": 1704916643.839096, "tokens": 30, "prompt_tokens": 22, "completion_tokens": 8}, "name": "OpenAI Chat Completion"}], "name": "run_input"}

Importing spans

The following program uses the Braintrust SDK in Python to import the spans generated by the previous script. Again, you can modify this program to fit the needs of your environment, e.g. to import spans from a different source or format.

import json
import sys
 
import braintrust
 
from autoevals import Factuality
 
 
def upload_tree(span, node, **kwargs):
    span.log(
        input=node.get("input"),
        output=node.get("output"),
        expected=node.get("expected"),
        metadata=node.get("metadata"),
        metrics=node.get("metrics"),
        **kwargs,
    )
    for c in node.get("children", []):
        with span.start_span(name=c.get("name")) as span:
            upload_tree(span, c)
 
 
if __name__ == "__main__":
    # This could be another container, like a log stream initialized
    # via braintrust.init_logger()
    experiment = braintrust.init("My Support App")
 
    factuality = Factuality()
    for line in sys.stdin:
        tree = json.loads(line)
        with experiment.start_span(name="task") as span:
            upload_tree(span, tree)
            with span.start_span(name="Factuality"):
                score = factuality(input=tree["input"], output=tree["output"], expected=tree["expected"])
            span.log(
                scores={
                    "factuality": score.score,
                },
                # This will merge the metadata from the factuality score with the
                # metadata from the tree.
                metadata={"factuality": score.metadata},
            )
 
    print(experiment.summarize())

Running traced functions in a ThreadPoolExecutor

The Python SDK uses context variables to hold the span state for traces. This means that if you run a traced function inside of a concurrent.futures.ThreadPoolExecutor, the span state will be lost.

Instead, you can use the TracedThreadPoolExecutor class provided by the Braintrust SDK. This class is a thin extension of concurrent.futures.ThreadPoolExecutor that captures and passes context variables to its workers.

import sys
 
import braintrust
import openai
 
braintrust.init_logger("math")
 
 
@braintrust.traced
def addition(client: openai.OpenAI):
    return client.chat.completions.create(
        model="gpt-4o-mini",
        messages=[{"role": "user", "content": "What is 1+1?"}],
    )
 
 
@braintrust.traced
def multiplication(client: openai.OpenAI):
    return client.chat.completions.create(
        model="gpt-4o-mini",
        messages=[{"role": "user", "content": "What is 1*1?"}],
    )
 
 
@braintrust.traced
def main():
    client = braintrust.wrap_openai(openai.OpenAI())
    with braintrust.TracedThreadPoolExecutor(max_workers=2) as e:
        try:
            a = e.submit(addition, client=client)
            m = e.submit(multiplication, client=client)
            a.result()
            m.result()
        except Exception as e:
            print("Failed", e, file=sys.stderr)
 
 
if __name__ == "__main__":
    main()

Tuning parameters

The SDK includes several tuning knobs that may prove useful for debugging.

• BRAINTRUST_SYNC_FLUSH: By default, the SDKs will log to the backend API in the background, asynchronously. Logging is automatically batched and retried upon encountering network errors. If you wish to have fine-grained control over when logs are flushed to the backend, you may set BRAINTRUST_SYNC_FLUSH=1. When true, flushing will only occur when you run Experiment.flush (or any of the other object flush methods). If the flush fails, the SDK will raise an exception which you can handle.
• BRAINTRUST_MAX_REQUEST_SIZE: The SDK logger batches requests to save on network roundtrips. The batch size is tuned for the AWS lambda gateway, but you may adjust this if your backend has a different max payload requirement.
• BRAINTRUST_DEFAULT_BATCH_SIZE: The maximum number of individual log messages that are sent to the network in one payload.
• BRAINTRUST_NUM_RETRIES: The number of times the logger will attempt to retry network requests before failing.
• BRAINTRUST_QUEUE_SIZE (Python only): The maximum number of elements in the logging queue. This value limits the memory usage of the logger. Logging additional elements beyond this size will block the calling thread. You may set the queue size to unlimited (and thus non-blocking) by passing BRAINTRUST_QUEUE_SIZE=0.
• BRAINTRUST_QUEUE_DROP_WHEN_FULL (Python only): Useful in conjunction with BRAINTRUST_QUEUE_SIZE. Change the behavior of the queue from blocking when it reaches its max size to dropping excess elements. This can be useful for guaranteeing non-blocking execution, at the cost of possibly dropping data.
• BRAINTRUST_QUEUE_DROP_EXCEEDING_MAXSIZE (Javascript only): Essentially a combination of BRAINTRUST_QUEUE_SIZE and BRAINTRUST_QUEUE_DROP_WHEN_FULL, which changes the behavior of the queue from storing an unlimited number of elements to capping out at the specified value. Additional elements are discarded.
• BRAINTRUST_FAILED_PUBLISH_PAYLOADS_DIR: Sometimes errors occur when writing records to the backend. To aid in debugging errors, you may set this environment variable to a directory of choice, and Braintrust will save any payloads it failed to publish to this directory.
• BRAINTRUST_ALL_PUBLISH_PAYLOADS_DIR: Analogous to BRAINTRUST_FAILED_PUBLISH_PAYLOADS_DIR, except that Braintrust will save all payloads to this directory.

Disabling logging

If you are not running an eval or logging, then the tracing code will be a no-op with negligible performance overhead. In other words, if you do not call initLogger/init_logger/init, in your code, then the tracing annotations are a no-op.

Trace data structures

A trace is a directed acyclic graph (DAG) of spans. Each span can have multiple parents, but most executions are a tree of spans. Currently, the UI only supports displaying a single root span, due to the popularity of this pattern.

Errors

If the Braintrust SDK cannot log for some reason (e.g. a network issue), then your application should not be affected. All logging operations run in a background thread, including api key validation, project/experiment registration, and flushing logs.

When errors occur, the SDK retries a few times before eventually giving up. You'll see loud warning messages when this occurs. And you can tune this behavior via the environment variables defined in Tuning parameters.