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Operate LangFlow Long Flow from Localhost and Remote APIs

2026-05-31 · guide · 12 min read

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Summary

This guide records the working setup for controlling a LangFlow long flow from Codex through APIs instead of browser automation. The stable local target is one LangFlow server on localhost:7860, with the long flow kept in the Starter Project and controlled through x-api-key authenticated REST calls.

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What This Solves

The goal is to avoid a messy setup where multiple LangFlow servers run on different ports such as 7861, 7863, and 7865. The working rule is simple: run one local LangFlow instance on localhost:7860, point Codex MCP tools at that instance, and use the same API pattern for remote LangFlow when needed. The current long flow is: 
Main Flow
Flow ID: 074add69-c4ca-4380-aff6-52b83e0239be
Local URL: http://localhost:7860/flow/074add69-c4ca-4380-aff6-52b83e0239be
Project ID: 23b5fba1-b555-4baa-9bb0-6a784d52aaf1
The current operational decision is also important: do not connect the expensive Agent branch for routine runs. It can consume too many tokens and trigger unnecessary tool loading.
Keep the long flow editable on the canvas, but keep expensive branches disconnected until they are explicitly needed.

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Who This Is For

This is for future me using Codex with LangFlow through MCP and REST APIs. It assumes LangFlow is installed locally, an API key exists, and Codex can run shell commands on the same machine. It is also useful when the same long flow must be operated in two places:
  • Local development on http://localhost:7860
  • Remote service such as https://langflow.yitwah.site

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Prerequisites

  • A local LangFlow virtual environment at /Users/yitwah/langflow-local/.venv
  • A LangFlow API key available in the shell as LANGFLOW_API_KEY
  • Codex MCP configuration at /Users/yitwah/.codex/config.toml
  • The long flow already present in LangFlow
  • curl, jq, and Python available locally
  • Optional remote LangFlow endpoint, for example https://langflow.yitwah.site
Check the local API key without printing it: 
test -n "$LANGFLOW_API_KEY" && echo "LANGFLOW_API_KEY is set"

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The Workflow

1

Run exactly one local LangFlow server

Use localhost:7860 as the only local LangFlow port for this long flow. Stop old servers on 7861, 7863, or 7865 before starting the stable one.
for port in 7860 7861 7865; do
  lsof -nP -iTCP:$port -sTCP:LISTEN
done
Start LangFlow in a detached screen session:
screen -S langflow-7860 -dm bash -lc 'cd /Users/yitwah/langflow-local && exec /Users/yitwah/langflow-local/.venv/bin/python -m langflow.__main__ run --host 127.0.0.1 --port 7860 --no-open-browser --log-level info > /tmp/langflow-7860.log 2>&1'
Confirm health:
curl -fsS http://127.0.0.1:7860/health_check
Expected result:
{"status":"ok","chat":"ok","db":"ok"}
2

Open the Main Flow directly

Avoid loading through the full project dashboard when working on a heavy canvas. Use the direct flow URL:
http://localhost:7860/flow/074add69-c4ca-4380-aff6-52b83e0239be
Direct opening avoids some workspace browsing overhead and keeps the workflow focused.
3

Configure Codex MCP for localhost

Point the starter project MCP proxy at localhost:7860:
[mcp_servers.lf-starter_project]
command = "uvx"
args = [
  "mcp-proxy",
  "--transport",
  "streamablehttp",
  "http://localhost:7860/api/v1/mcp/project/23b5fba1-b555-4baa-9bb0-6a784d52aaf1/streamable"
]
startup_timeout_sec = 120.0
Point the admin MCP at the same local base URL:
[mcp_servers.langflow-admin.env]
LANGFLOW_BASE_URL = "http://localhost:7860"
LANGFLOW_USE_BROWSEROS = "false"
BROWSEROS_MCP_URL = "http://127.0.0.1:9000/mcp"
Store API keys in environment variables or secure config, not in guide text.
4

Use REST APIs for local flow operations

List flows:
curl --compressed -sS \
  -H "x-api-key: $LANGFLOW_API_KEY" \
  "http://localhost:7860/api/v1/flows/?get_all=true" | jq 'length'
Fetch the long flow:
FLOW=074add69-c4ca-4380-aff6-52b83e0239be
curl --compressed -sS \
  -H "x-api-key: $LANGFLOW_API_KEY" \
  "http://localhost:7860/api/v1/flows/$FLOW" \
  -o /tmp/main-flow.json
Update a complete flow JSON:
FLOW=074add69-c4ca-4380-aff6-52b83e0239be
curl --compressed -sS \
  -H "x-api-key: $LANGFLOW_API_KEY" \
  -H "Content-Type: application/json" \
  -X PUT \
  "http://localhost:7860/api/v1/flows/$FLOW" \
  --data-binary @/tmp/main-flow.json
5

Run or minimally build the flow through API

Run the flow:
FLOW=074add69-c4ca-4380-aff6-52b83e0239be
curl --compressed -sS \
  -H "x-api-key: $LANGFLOW_API_KEY" \
  -H "Content-Type: application/json" \
  "http://localhost:7860/api/v1/run/$FLOW?stream=false" \
  -d '{"inputs":{"input_value":"/Users/yitwah/Projects/pdf2latex/pdf/test.pdf"},"tweaks":{}}'
For a lighter test, build only until a specific component:
FLOW=074add69-c4ca-4380-aff6-52b83e0239be
curl --compressed -sS \
  -H "x-api-key: $LANGFLOW_API_KEY" \
  -H "Content-Type: application/json" \
  "http://localhost:7860/api/v1/build/$FLOW/flow?stop_component_id=CustomComponent-Kx7jD" \
  -d '{"inputs":{"input_value":"/Users/yitwah/Projects/pdf2latex/pdf/test.pdf"},"tweaks":{}}'
The build endpoint returns a job ID. Stream events like this:
JOB_ID="replace-with-returned-job-id"
curl --compressed -sS -N \
  -H "x-api-key: $LANGFLOW_API_KEY" \
  "http://localhost:7860/api/v1/build/$JOB_ID/events"
6

Operate the remote LangFlow with the same pattern

For remote work, change only the base URL and API key source:
export LANGFLOW_REMOTE_BASE_URL="https://langflow.yitwah.site"
export LANGFLOW_REMOTE_API_KEY="set-this-in-your-shell-or-secret-store"
Then use:
curl --compressed -sS \
  -H "x-api-key: $LANGFLOW_REMOTE_API_KEY" \
  "$LANGFLOW_REMOTE_BASE_URL/api/v1/flows/?get_all=true"
Remote MCP streamable endpoint pattern:
{
  "mcpServers": {
    "lf-starter_project": {
      "command": "uvx",
      "args": [
        "mcp-proxy",
        "--transport",
        "streamablehttp",
        "https://langflow.yitwah.site/api/v1/mcp/project/05314765-c54d-49c5-bc25-3ae5b302ebad/streamable"
      ]
    }
  }
}
7

Keep expensive Agent branches disconnected

In the current long flow, avoid connecting edges into Agent-hNNgH unless the task explicitly needs it.Verification command:
FLOW=074add69-c4ca-4380-aff6-52b83e0239be
curl --compressed -sS \
  -H "x-api-key: $LANGFLOW_API_KEY" \
  "http://localhost:7860/api/v1/flows/$FLOW" \
  | jq '.data.edges | map(select(.source=="Agent-hNNgH" or .target=="Agent-hNNgH")) | length'
Expected result:
0

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Common Failure Modes

If the browser shows misc.fetchErrorMessage or misc.fetchErrorDescription, the frontend health check failed or the browser session is stale. First check http://localhost:7860/health_check, then clear site data for localhost:7860 or open a new private window.
If LangFlow reports sqlite3.OperationalError: database is locked, there are usually multiple LangFlow processes pointing at the same SQLite database. Stop duplicate ports and keep only 7860 running.
If red boxes show OSError Details: 5, inspect the build event stream. In the long flow session, this came from Run Flow tool nodes connected to the Agent. The fix was to disconnect those Run Flow -> Agent tools edges.
Do not connect PDF Path Injector -> Agent or Run Flow -> Agent tools during ordinary PDF processing. The Agent path is token-heavy and may run subflow tools even when the main PDF metadata path already works.
Use stopped builds to test individual components. They are faster and safer than running the entire long flow while debugging a single edge or input block.

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Final Checklist

  • curl http://127.0.0.1:7860/health_check returns {"status":"ok","chat":"ok","db":"ok"}
  • 7861, 7863, and 7865 are not running old LangFlow servers
  • http://localhost:7860/flow/074add69-c4ca-4380-aff6-52b83e0239be opens the long flow
  • LANGFLOW_API_KEY is set in the shell or secure Codex config
  • The MCP starter project URL uses localhost:7860
  • The admin MCP base URL uses http://localhost:7860
  • Agent edge count is 0 unless an Agent run is explicitly desired
  • Remote operations use LANGFLOW_REMOTE_BASE_URL and LANGFLOW_REMOTE_API_KEY

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What To Remember

The durable rule is: one long flow, one local port, one API pattern. Keep local development on localhost:7860, use x-api-key for API operations, and do not let heavy Agent branches become part of the default run path.

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Metadata

Quick Reference

Type: guide
Tags: langflow · api · mcp · codex · workflow
Related: [[LangFlow]] · [[Codex MCP]] · [[API automation]]