LangSmith Fetch

LangSmith Fetch is a command-line interface (CLI) tool for retrieving trace data (runs, traces, and threads) from your LangSmith projects. It allows you to use LangSmith’s tracing and debugging features directly in your terminal and development workflows. You can use LangSmith Fetch for the following use cases:

Immediate debugging: Fetch the most recent trace of a failed or unexpected agent run with a single command.
Bulk export for analysis: Export large numbers of traces or entire conversation threads to JSON files for offline analysis, building evaluation datasets, or regression tests.
Terminal-based workflows: Integrate trace data into your existing tools; for example, piping output to Unix utilities like jq, or feeding traces into an AI coding assistant for automated analysis.

Installation

pip install langsmith-fetch

Setup

Set your LangSmith API key and project name:

export LANGSMITH_API_KEY=lsv2_...
export LANGSMITH_PROJECT=your-project-name

The CLI will automatically fetch traces or threads in LANGSMITH_PROJECT. Replace your-project-name with the name of your LangSmith project (if it doesn’t exist, it will be created automatically on first use).

langsmith-fetch only requires the LANGSMITH_PROJECT environment variable. It automatically looks up the project UUID and saves both to ~/.langsmith-cli/config.yaml. You can also specify a project by its UUID via a CLI flag.

Use with a coding agent

After you’ve installed and set up langsmith-fetch, use your coding agent to ask questions like the following:

Use langsmith-fetch to analyze the last 3 threads from my LangSmith project for potential improvements

Many agents will use the langsmith-fetch --help command to understand how to use the CLI and complete your request.

Find project and trace IDs

In most cases, you won’t need to find IDs manually (the CLI uses your project name and latest traces by default). However, if you want to fetch a specific item by ID, you can find them in the LangSmith UI:

Project UUID: Each project has a unique ID (UUID). You can find it in the project’s URL or by hovering over ID next to the project’s name. This UUID can be used with the --project-uuid flag on CLI commands
Trace ID: Every trace (single execution) has an ID. In the Runs view, click on a specific run to see its Trace ID (copyable from the trace details panel). You can use langsmith-fetch trace <trace-id> to retrieve that exact trace if you have the ID.

Usage

After installation and setup, you can use the langsmith-fetch command to retrieve traces or threads. The general usage is:

langsmith-fetch COMMAND [ARGUMENTS] [OPTIONS]

LangSmith Fetch provides the following commands to fetch either single items or in bulk:

Command	Fetches	Output location
`trace <id>`	A specific trace by ID	Prints to stdout (or to a file with `--file`)
`thread <id>`	A specific thread by ID	Prints to stdout (or to a file with `--file`)
`traces [directory]`	Recent traces from the project (multiple)	Saves each trace as a JSON file in the given directory, or prints to stdout if no directory is provided. Tip: Using a directory is recommended for bulk exports.
`threads [directory]`	Recent threads from the project (multiple)	Saves each thread as a JSON file in the given directory, or prints to stdout if no directory is provided.

Traces are fetched chronologically with most recent first.

Options

The commands support additional flags to filter and format the output:

Option / Flag	Applies to	Description	Default
`-n, --limit <int>`	`traces`, `threads`	Maximum number of traces/threads to fetch. Use this to limit how many items you retrieve (e.g., the last 5 traces).	1 (if not specified)
`--last-n-minutes <int>`	`traces`, `threads`	Only fetch items from the last N minutes. This is useful to get recent data (e.g.,`--last-n-minutes 30` for the past half hour).	(no time filter)
`--since <timestamp>`	`traces`, `threads`	Only fetch items since a specific time. Provide an ISO 8601 timestamp (e.g.,`2025-12-01T00:00:00Z`) to get data after that time.	(no time filter)
`--project-uuid <uuid>`	`trace, thread, traces, threads`	Manually specify the project by UUID (overrides the `LANGSMITH_PROJECT` env setting). Use this if you want to fetch from a different project without changing your env var.	From env/config
`--filename-pattern <text>`	`traces`, `threads`	Pattern for output filenames when saving multiple files. You can use placeholders like `{trace_id}`, `{thread_id}`, `{index}`.	`{trace_id}.json` or `{thread_id}.json`
`--format <type>`	All commands	Output format: `pretty`, `json`, or `raw`. (Refer to Output formats for details.)	`pretty`
`--file <path>`	`trace`, `thread`	Save the fetched trace/thread to a file instead of printing it.	(stdout)
`--include-metadata`	`traces` (bulk fetch)	Include run metadata in the output (such as tokens used, execution time, status, costs). This will add a `"metadata"` section to each trace’s JSON.	Off by default
`--include-feedback`	`traces` (bulk fetch)	Include any feedback entries attached to the runs. Enabling this will make an extra API call for each trace to fetch feedback data.	Off by default
`--max-concurrent <int>`	`traces`, `threads`	Maximum concurrent fetch requests. Tune this if you are fetching a large number of items; increasing it may speed up retrieval but 5–10 is recommended to avoid API overload.	5
`--no-progress`	`traces`, `threads`	Disable the progress bar output. By default a progress indicator is shown when fetching multiple items; use this flag to hide it (useful for non-interactive scripts).	Progress bar on

Output formats

The --format option controls how the fetched data is displayed:

pretty (default): A human-readable view with rich text formatting for easy inspection in the terminal. This format is great for quick debugging of a single trace or thread. By default:
langsmith-fetch trace <trace-id>
Explicitly specify the format:
langsmith-fetch trace <trace-id> --format pretty
json: Well-formatted JSON output with syntax highlighting. Use this if you want to examine the raw data structure or pipe it into JSON processing tools.
langsmith-fetch trace <trace-id> --format json
raw: Compact JSON with no extra whitespace. This is useful for piping the output to other programs (e.g., using jq or saving directly) without extra formatting.
langsmith-fetch trace <trace-id> --format raw | jq '.[] | select(.role=="user")'

Fetch a trace or thread

You can fetch a single thread or trace with the ID. The command will output to the terminal by default:

langsmith-fetch trace <trace-id>

langsmith-fetch thread <thread-id>

Output from a single trace fetch in default pretty format

You can optionally redirect the thread or trace data to a file using the --file option.

Fetch multiple

For bulk fetches of traces or threads, we recommend specifying a target directory path. Each fetched trace or thread will be saved as a separate JSON file in that folder, making it easy to browse or process them later.

You can specify a destination directory for the bulk commands (traces/threads). For example, the following command will save the 10 most recent traces as JSON files in the my-traces-data directory:

langsmith-fetch traces ./my-traces-data --limit 10

langsmith-fetch threads ./my-thread-data --limit 10

If you omit the directory and --limit, the tool will output the results of the most recent, single trace to your terminal. When sending to a directory, files will be named in the following way:

Default: Files named by trace ID (e.g., 3b0b15fe-1e3a-4aef-afa8-48df15879cfe.json).
Custom pattern: Use --filename-pattern with placeholders:
- {trace_id}: Trace ID (default: {trace_id}.json).
- {index} or {idx}: Sequential number starting from 1.
- Format specs supported: {index:03d} for zero-padded numbers.

Include metadata and feedback

You can include run metadata and any feedback associated with the trace:

langsmith-fetch traces --limit 1 --include-metadata --include-feedback

RUN METADATA
============================================================
Status: success
Start Time: 2025-12-12T18:05:47.558274
End Time: 2025-12-12T18:05:48.811072
Duration: 1252ms

Token Usage:
  Prompt: 15
  Completion: 88
  Total: 103

Costs:
  Total: $0.00014
  Prompt: $0.00001
  Completion: $0.00013

Custom Metadata:
  LANGSMITH_PROJECT: weather-demo
  LANGSMITH_TRACING: true
  ls_run_depth: 0

Feedback Stats:
  correctness: {'n': 1, 'avg': 1.0, 'stdev': 0.0, 'errors': 0, 'show_feedback_arrow': False, 'comments': [''], 'sources':
['{"type":"app","metadata":null,"user_id":"d5ee8d42-a274-4f32-9c35-b765287fe5ec","ls_user_id":"ac375f5f-0da0-44c1-82a2-0ecfd6ecac27"}'],
'session_min_score': 1.0, 'session_max_score': 1.0, 'values': {}, 'contains_thread_feedback': False}
  note: {'n': 0, 'avg': None, 'stdev': None, 'errors': 0, 'show_feedback_arrow': False, 'comments': ['The answer should be more specific on rainfall
totals.'], 'sources':
['{"type":"app","metadata":null,"user_id":"d5ee8d42-a274-4f32-9c35-b765287fe5ec","ls_user_id":"ac375f5f-0da0-44c1-82a2-0ecfd6ecac27"}'],
'session_min_score': None, 'session_max_score': None, 'values': {}, 'contains_thread_feedback': False}
...

Override the configured tracing project

To fetch traces from a different project than the one configured with LANGSMITH_PROJECT, use the --project-uuid option:

langsmith-fetch traces --project-uuid <project-id> --limit 3

Running this command will just fetch traces from that project, it will not modify the LangSmith project already configured in ~/.langsmith-cli/config.yaml.

Export to files

You can fetch traces or full threads and export to a file:

langsmith-fetch threads ./my_threads --since 2025-12-01T00:00:00Z

This command retrieves all threads that have occurred since December 1, 2025, saving each conversation as a JSON file under ./my_threads. This is useful for exporting chat transcripts or building regression tests on multi-turn conversations. You could also use --limit with threads to fetch a specific number of recent threads, and --last-n-minutes works here as well.

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Tracing setup

Configuration & troubleshooting

Viewing & managing traces

Automations

Feedback & evaluation

Monitoring & alerting

Data type reference

Installation

Setup

Use with a coding agent

Find project and trace IDs

Usage

Options

Output formats

Fetch a trace or thread

Fetch multiple

Include metadata and feedback

Override the configured tracing project

Export to files

​Installation

​Setup

​Use with a coding agent

​Find project and trace IDs

​Usage

​Options

​Output formats

​Fetch a trace or thread

​Fetch multiple

​Include metadata and feedback

​Override the configured tracing project

​Export to files

Installation

Setup

Use with a coding agent

Find project and trace IDs

Usage

Options

Output formats

Fetch a trace or thread

Fetch multiple

Include metadata and feedback

Override the configured tracing project

Export to files