Flow trigger endpoints

import CodeSnippet from '@site/src/components/CodeSnippet'; import exampleApiFlowsRunRunFlow from '!!raw-loader!@site/docs/API-Reference/curl-examples/api-flows-run/run-flow.sh'; import exampleApiFlowsRunStreamLlmTokenResponses from '!!raw-loader!@site/docs/API-Reference/curl-examples/api-flows-run/stream-llm-token-responses.sh'; import exampleApiFlowsRunRequestExampleWithAllHeadersAndParameters from '!!raw-loader!@site/docs/API-Reference/curl-examples/api-flows-run/request-example-with-all-headers-and-parameters.sh'; import exampleApiFlowsRunPassGlobalVariablesInRequestHeaders from '!!raw-loader!@site/docs/API-Reference/curl-examples/api-flows-run/pass-global-variables-in-request-headers.sh'; import exampleApiFlowsRunWebhookRunFlow from '!!raw-loader!@site/docs/API-Reference/curl-examples/api-flows-run/webhook-run-flow.sh'; import resultApiFlowsRunResultWebhookRunFlow from '!!raw-loader!@site/docs/API-Reference/curl-examples/api-flows-run/result-webhook-run-flow.json'; import examplePythonApiFlowsRunRunFlow from '!!raw-loader!@site/docs/API-Reference/python-examples/api-flows-run/run-flow.py'; import exampleJavascriptApiFlowsRunRunFlow from '!!raw-loader!@site/docs/API-Reference/javascript-examples/api-flows-run/run-flow.js'; import examplePythonApiFlowsRunStreamLlmTokenResponses from '!!raw-loader!@site/docs/API-Reference/python-examples/api-flows-run/stream-llm-token-responses.py'; import exampleJavascriptApiFlowsRunStreamLlmTokenResponses from '!!raw-loader!@site/docs/API-Reference/javascript-examples/api-flows-run/stream-llm-token-responses.js'; import examplePythonApiFlowsRunRequestExampleWithAllHeadersAndParameters from '!!raw-loader!@site/docs/API-Reference/python-examples/api-flows-run/request-example-with-all-headers-and-parameters.py'; import exampleJavascriptApiFlowsRunRequestExampleWithAllHeadersAndParameters from '!!raw-loader!@site/docs/API-Reference/javascript-examples/api-flows-run/request-example-with-all-headers-and-parameters.js'; import examplePythonApiFlowsRunPassGlobalVariablesInRequestHeaders from '!!raw-loader!@site/docs/API-Reference/python-examples/api-flows-run/pass-global-variables-in-request-headers.py'; import exampleJavascriptApiFlowsRunPassGlobalVariablesInRequestHeaders from '!!raw-loader!@site/docs/API-Reference/javascript-examples/api-flows-run/pass-global-variables-in-request-headers.js'; import examplePythonApiFlowsRunWebhookRunFlow from '!!raw-loader!@site/docs/API-Reference/python-examples/api-flows-run/webhook-run-flow.py'; import exampleJavascriptApiFlowsRunWebhookRunFlow from '!!raw-loader!@site/docs/API-Reference/javascript-examples/api-flows-run/webhook-run-flow.js';

import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem';

Use the /run and /webhook endpoints to run flows.

To create, read, update, and delete flows, see Flow management endpoints.

Run flow

:::tip Langflow automatically generates Python, JavaScript, and curl code snippets for the /v1/run/$FLOW_ID endpoint for all flows. For more information, see Generate API code snippets. :::

Execute a specified flow by ID or name. Flow IDs can be found on the code snippets on the API access pane or in a flow's URL.

The following example runs the Basic Prompting template flow with flow parameters passed in the request body. This flow requires a chat input string (input_value), and uses default values for all other parameters.

The response from /v1/run/$FLOW_ID includes metadata, inputs, and outputs for the run.

The following example illustrates a response from a Basic Prompting flow:

{
  "session_id": "chat-123",
  "outputs": [{
    "inputs": {
      "input_value": "Tell me about something interesting!"
    },
    "outputs": [{
      "results": {
        "message": {
          "text": "Sure! Have you ever heard of the phenomenon known as \"bioluminescence\"? It's a fascinating natural occurrence where living organisms produce and emit light. This ability is found in various species, including certain types of jellyfish, fireflies, and deep-sea creatures like anglerfish.\n\nBioluminescence occurs through a chemical reaction in which a light-emitting molecule called luciferin reacts with oxygen, catalyzed by an enzyme called luciferase. The result is a beautiful glow that can serve various purposes, such as attracting mates, deterring predators, or luring prey.\n\nOne of the most stunning displays of bioluminescence can be seen in the ocean, where certain plankton emit light when disturbed, creating a mesmerizing blue glow in the water. This phenomenon is often referred to as \"sea sparkle\" and can be seen in coastal areas around the world.\n\nBioluminescence not only captivates our imagination but also has practical applications in science and medicine, including the development of biosensors and imaging techniques. It's a remarkable example of nature's creativity and complexity!",
          "sender": "Machine",
          "sender_name": "AI",
          "session_id": "chat-123",
          "timestamp": "2025-03-03T17:17:37+00:00",
          "flow_id": "d2bbd92b-187e-4c84-b2d4-5df365704201",
          "properties": {
            "source": {
              "id": "OpenAIModel-d1wOZ",
              "display_name": "OpenAI",
              "source": "gpt-4o-mini"
            },
            "icon": "OpenAI"
          },
          "component_id": "ChatOutput-ylMzN"
        }
      }
    }]
  }]
}

If you are parsing the response in an application, you most likely need to extract the relevant content from the response, rather than pass the entire response back to the user. For an example of a script that extracts data from a Langflow API response, see the Quickstart.

Stream LLM token responses

With /v1/run/$FLOW_ID, the flow is executed as a batch with optional LLM token response streaming.

To stream LLM token responses, append the ?stream=true query parameter to the request:

LLM chat responses are streamed back as token events, culminating in a final end event that closes the connection.

The following example is truncated to illustrate a series of token events as well as the final end event that closes the LLM's token streaming response:

{"event": "add_message", "data": {"timestamp": "2025-03-03T17:20:18", "sender": "User", "sender_name": "User", "session_id": "chat-123", "text": "Tell me about something interesting!", "files": [], "error": false, "edit": false, "properties": {"text_color": "", "background_color": "", "edited": false, "source": {"id": null, "display_name": null, "source": null}, "icon": "", "allow_markdown": false, "positive_feedback": null, "state": "complete", "targets": []}, "category": "message", "content_blocks": [], "id": "0103a21b-ebf7-4c02-9d72-017fb297f812", "flow_id": "d2bbd92b-187e-4c84-b2d4-5df365704201"}}

{"event": "add_message", "data": {"timestamp": "2025-03-03T17:20:18", "sender": "Machine", "sender_name": "AI", "session_id": "chat-123", "text": "", "files": [], "error": false, "edit": false, "properties": {"text_color": "", "background_color": "", "edited": false, "source": {"id": "OpenAIModel-d1wOZ", "display_name": "OpenAI", "source": "gpt-4o-mini"}, "icon": "OpenAI", "allow_markdown": false, "positive_feedback": null, "state": "complete", "targets": []}, "category": "message", "content_blocks": [], "id": "27b66789-e673-4c65-9e81-021752925161", "flow_id": "d2bbd92b-187e-4c84-b2d4-5df365704201"}}

{"event": "token", "data": {"chunk": " Have", "id": "27b66789-e673-4c65-9e81-021752925161", "timestamp": "2025-03-03 17:20:18 UTC"}}

{"event": "token", "data": {"chunk": " you", "id": "27b66789-e673-4c65-9e81-021752925161", "timestamp": "2025-03-03 17:20:18 UTC"}}

{"event": "token", "data": {"chunk": " ever", "id": "27b66789-e673-4c65-9e81-021752925161", "timestamp": "2025-03-03 17:20:18 UTC"}}

{"event": "token", "data": {"chunk": " heard", "id": "27b66789-e673-4c65-9e81-021752925161", "timestamp": "2025-03-03 17:20:18 UTC"}}

{"event": "token", "data": {"chunk": " of", "id": "27b66789-e673-4c65-9e81-021752925161", "timestamp": "2025-03-03 17:20:18 UTC"}}

{"event": "token", "data": {"chunk": " the", "id": "27b66789-e673-4c65-9e81-021752925161", "timestamp": "2025-03-03 17:20:18 UTC"}}

{"event": "token", "data": {"chunk": " phenomenon", "id": "27b66789-e673-4c65-9e81-021752925161", "timestamp": "2025-03-03 17:20:18 UTC"}}

{"event": "end", "data": {"result": {"session_id": "chat-123", "message": "Sure! Have you ever heard of the phenomenon known as \"bioluminescence\"?..."}}}

Run endpoint headers

Run endpoint parameters

Request example with all headers and parameters

Pass global variables in request headers {#pass-global-variables-in-headers}

You can pass global variables to your flow using HTTP headers with the format X-LANGFLOW-GLOBAL-VAR-{VARIABLE_NAME}.

Variables passed in headers take precedence over OS environment variables. If a variable is provided in both a header and an environment variable, the header value is used. Variables are only available during this specific request execution and aren't persisted.

Variable names are automatically converted to uppercase. For example, X-LANGFLOW-GLOBAL-VAR-api-key becomes API_KEY in your flow.

You don't need to create these variables in Langflow's Global Variables section first. Pass any variable name using this header format.

If your flow components reference variables that aren't provided in headers or your Langflow database, the flow fails by default. To avoid this, you can set LANGFLOW_FALLBACK_TO_ENV_VAR=True in your .env file, which allows the flow to use values from OS environment variables if they aren't otherwise specified.

Webhook run flow

Use the /webhook endpoint to start a flow by sending an HTTP POST request.

:::tip After you add a Webhook component to a flow, open the API access pane, and then click the Webhook curl tab to get an automatically generated POST /webhook request for your flow. For more information, see Trigger flows with webhooks. :::

Deprecated flow trigger endpoints

The following endpoints are deprecated and replaced by the /run endpoint:

• /process
• /predict