Webhook: let outside systems call into n8n

Why Webhook is the last piece of the puzzle

Lay out the trigger types from the last few chapters and one thing stands out:

• Manual Trigger (Chapter 10) — the workflow only moves when you press the button.
• Schedule Trigger — the time comes and the workflow moves by itself.
• Gmail / Slack / Sheets Trigger (Chapter 11) — the SaaS side has a new event and n8n polls for it on a timer to bring it back.
• The HTTP Request node (Chapter 12) — n8n goes out and calls someone else's API.

What they share: n8n is always the one making the move. One mode is missing — "an outside system wants to wake your workflow up". That is exactly what the Webhook node does.

Webhook comes up in far more situations than you would think:

• Someone fills in the contact form on your company website, and the data goes into Google Sheets, a Slack notification goes to sales, and a record goes into the CRM.
• Your LINE Official Account receives a customer message, AI Agent (Chapter 21) produces the reply, and it goes back to LINE.
• A Home Assistant door sensor detects "someone came home" and triggers an n8n workflow that logs it to Notion and turns off the company VPN while it is at it.
• Someone opens a PR on GitHub: notify QA, open a Jira ticket, run a round of internal lint.
• A new order arrives through Stripe / ECPay payments: write it into the ERP, send the invoice, add loyalty points.

Put simply: if the other system has a "webhook" or "callback URL" field you can fill in, it can call into n8n. This chapter covers how to receive the call, how to configure it, how to reply, and how to keep strangers from hammering it.

A webhook is your workflow's doorbell

The plainest way to put it:

• Schedule Trigger is an alarm clock — it goes off when the time comes.
• The HTTP Request node is you making a phone call — you go out to ask someone something.
• The Webhook node is a doorbell — someone arrives, presses it, and you know about it.

When you add a Webhook node to a workflow, n8n hands you a URL that looks like this:

https://n8n.woowtech.io/webhook/form-abc123

Anyone (a person, a server, LINE, HA, a curl command) who calls that URL triggers your workflow. Everything that comes in (body, query string, headers) becomes the $json of the workflow's first item — so the nodes after it can pull the values out with an expression ({{ $json.name }} and so on).

In other words, the Webhook node turns your workflow into a simple HTTP API. Any service that knows the URL can trigger it. That is also why Zapier / Make have a "Webhooks" trigger of their own — it is the bridge every automation platform shares.

Two URLs: how Test and Production differ

Open the Webhook node's settings panel and you see two URLs — the first big trap for beginners.

The differences between the two URLs are small but they matter:

• The two URLs have different paths — the Test URL is usually /webhook-test/xxx and Production is /webhook/xxx. Look carefully and pick the right one when you copy from the node panel.
• The Test URL takes one event per trigger and then closes itself, which suits tweaking fields and reading the schema.
• The Production URL does not show up as the live preview in Executions — to see the records of runs that really happened, open the Executions tab.

Hands-on: catch form data and write it to Google Sheets

The most classic and most useful starter example: expose one URL, let a web form POST what the user typed, and have n8n write it into Google Sheets automatically. Once it works you can wire it straight to the contact form on your own site or landing page.

1. Create a new workflow and pick Webhook as the first node

   Top right + Add workflow → you land on an empty canvas → click the + in the middle → search the nodes panel for Webhook (under the Triggers category). Add it.

2. Set the HTTP Method and the Path

   Once the Webhook node is open:

   • Set HTTP Method to POST — a form sending data in uses POST by default.
   • Give Path any memorable English name, for example form-contact. It is appended to the end of the URL.

   Once that is set, the bottom of the node panel shows both URLs:

   Test URL:       https://n8n.woowtech.io/webhook-test/form-contact
   Production URL: https://n8n.woowtech.io/webhook/form-contact

3. Press Listen for test event and call it once with curl

   Press Listen for test event at the top right of the Webhook node — the node goes into waiting mode (it ends by itself after the first event, and in practice it stops after about two minutes if no event arrives). Open a terminal and use curl to send fake data to the Test URL:

   curl -X POST https://n8n.woowtech.io/webhook-test/form-contact \
     -H "Content-Type: application/json" \
     -d '{"name":"Wang Xiaoming","email":"[email protected]","message":"I would like a quote"}'

   Back on the n8n canvas, the Webhook node turns green and the output panel on the right shows the JSON you just sent. Once you see the data arrive, this step is done.

4. Wire up a Google Sheets node: Append Row

   Add a Google Sheets node after the Webhook node. Set Operation to Append Row in Sheet. Pick your credential (create one the first time; see Chapter 13). Choose a spreadsheet and a sheet (with the columns name, email, message, received_at already created).

   Switch every field in the Columns block to Expression mode and map them like this:

   name          →  {{ $json.body.name }}
   email         →  {{ $json.body.email }}
   message       →  {{ $json.body.message }}
   received_at   →  {{ $now.toISO() }}

   Note that the Webhook node keeps the body under $json.body, the query string under $json.query, and the headers under $json.headers.

5. Execute step and confirm the Sheet really has a new row

   Press Execute step on the Google Sheets node — it sends the item the Webhook just received. Open Google Sheets and check whether a row with that data appeared. If it did, the whole chain is connected.

   

6. Save, then switch Active on at the top right

   Press Save at the top right. Then flip the Active toggle at the top right to on — this step matters, because without it the Production URL is a 404.

7. Verify by calling the Production URL once

   Back in the terminal, call the Production URL instead (replace /webhook-test/ with /webhook/):

   curl -X POST https://n8n.woowtech.io/webhook/form-contact \
     -H "Content-Type: application/json" \
     -d '{"name":"Li Xiaohua","email":"[email protected]","message":"Live submission"}'

   Another row appears in the Sheet — this URL is now ready to hand to an outside frontend engineer or a customer. For the history, go to the Executions tab in the sidebar.

HTTP methods: which one to use when

The Webhook node's HTTP Method dropdown offers GET / POST / PUT / PATCH / DELETE / HEAD. In practice you only use the first two often; the rest come up when you are building a REST-style API.

The wrong Method gives you a 404 — the outside system calls with POST while your Webhook node is set to GET, and n8n answers 404 outright (because as far as it is concerned, "this path has no POST route"). When incoming data is stuck, the first thing to do is confirm that both sides use the same Method.

Response modes: what n8n sends back to the caller

The Webhook node's Respond option decides "what HTTP response n8n returns once an outside call comes in". This matters — services like LINE, Slack and Stripe all read what you return to judge whether the webhook succeeded. Answer wrong and they may retry (which gives you duplicate runs) or disable your webhook outright.

The Respond to Webhook node is the key to that third mode — put it after whichever node you want to answer from (it does not have to be the last one) and you can set:

• Respond With — the shape of the answer: JSON, Text, Binary File, Redirect, JWT Token, No Data, All Incoming Items, First Incoming Item.
• Response Code — type the number yourself. Common ones: 200 (success), 201 (Created), 400 (client error), 500 (server error).
• Response Headers — for example Content-Type: application/json, or CORS-related headers.

Watch out: the Respond to Webhook node only handles the first incoming item; even if the node before it emits many, only the first one is used for the reply. A second Respond to Webhook node in the same workflow is ignored. If the workflow runs to the end without passing through any Respond to Webhook node, n8n answers a standard 200 by itself; if it errors on the way and never reaches the node, it answers 500.

Services that commonly call your webhook

Almost every modern SaaS has a webhook feature — when they have an event to tell you about, they POST to a URL you name. Put your n8n Webhook node's Production URL in that field and the two are wired together. Here are the ones you meet most often:

The rule that holds everywhere: every service sends its webhook in its own JSON schema — trigger it once by hand with the Test URL, pull the body up and read the field paths, and only then write the nodes downstream. Writing $json.body.foo blind usually gives you undefined.

Add auth so nobody can guess the URL and hammer it

Once a Webhook URL is out there, anyone can call it. Someone malicious can stuff junk into your Sheet, fire an expensive AI Agent, or send spam LINE messages. There are several ways to protect it, from the simplest to the most advanced:

Worked example: a LINE bot calls n8n and AI Agent replies

Combine Webhook + AI Agent (Chapter 21) + HTTP Request (Chapter 12) into the complete chain "a customer sends a message on LINE, n8n produces a reply with GPT, and it goes back to the customer automatically" — everything from the earlier chapters comes together here in one real build.

1. Create a Messaging API channel in the LINE Developers Console

   Go to developers.line.biz and sign in → create a Provider → add a Messaging API channel. Fill in the basics and submit.

2. Get the Channel Secret and the Access Token

   Once the channel exists, go to the Basic settings tab and copy down the Channel Secret; at the bottom of the Messaging API tab, press Issue under Channel Access Token to generate one and copy it. Both of these go into n8n Credentials in a moment.

3. New n8n workflow: a Webhook node on POST, and the URL it gives you

   Create a new workflow in n8n and add a Webhook node: Method = POST, Path = line-bot, Response = Immediately (LINE wants a 200 within 3 seconds). Copy the Production URL — but you cannot use it yet, because the workflow is not Active. For now, press Listen for test event and build against the Test URL.

4. On the LINE side, put the n8n URL in Webhook URL

   Back in the LINE Console on the Messaging API tab → Webhook settings → paste the n8n Test URL → turn on Use webhook. Press Verify and it should say Success (LINE really does call it once).

5. Add the LINE bot as a friend on your phone and send it a message

   Scan the QR code shown in the LINE Console with your phone to add the Official Account as a friend, and send it a "hello". Back on the n8n canvas, the Webhook node turns green and the output shows LINE's payload. Find the path to the message text; it is usually:

   {{ $json.body.events[0].message.text }}      →  the text the user typed
   {{ $json.body.events[0].replyToken }}        →  the token you reply with
   {{ $json.body.events[0].source.userId }}     →  the user's ID

6. Add an AI Agent node to produce the reply

   Add an AI Agent node (Chapter 21). Use an expression in the Text field to bring in the user's message: {{ $json.body.events[0].message.text }}. Attach a Chat Model (OpenAI GPT-4o mini or another). Add Memory if you want it to remember the conversation.

7. Add an HTTP Request node to call the LINE Reply API

   Add HTTP Request: Method = POST, URL = https://api.line.me/v2/bot/message/reply, Authentication set to Header Auth, carrying Authorization: Bearer <your-channel-access-token>. Use JSON for the body:

   {
     "replyToken": "{{ $('Webhook').item.json.body.events[0].replyToken }}",
     "messages": [
       { "type": "text", "text": "{{ $json.output }}" }
     ]
   }

   $('Webhook') reaches back to the Webhook node for the replyToken; $json.output is the reply AI Agent has just produced.

8. Save + Active, then switch the LINE webhook to the Production URL

   Save, then switch Active on. Back in the LINE Console, change the Webhook URL from the Test URL to the Production URL (/webhook/line-bot). Send another message from your phone — the answer comes back in a second.

Common pitfalls

1. You called the Test URL and nothing happened; n8n received nothing

   Two causes: (a) you did not press Listen for test event — the Test URL only lives in listen mode; (b) the listen session expired (it ends after one event, and in practice it also stops when nothing arrives for a while) — just press it again. Also check that you picked the right URL — when you copy, make sure it is the /webhook-test/ one.

2. Calling the Production URL returns 404 Not Found

   Almost always the workflow is not Active — while the toggle at the top right is off, the Production URL is a 404. The fix: save, then switch Active on at the top right. If it still returns 404 with Active on, check that the Path matches what you are calling (it is case sensitive, and a stray space breaks it).

3. The webhook arrives but the body is empty

   Their request set no Content-Type, or set it to text/plain instead of application/json — n8n will not parse it for you. Ask them to add the Content-Type: application/json header when they call; or turn on Options → Raw Body on the Webhook node and parse it yourself in a Code node. Also note that the n8n Webhook node caps a single payload at 16MB — anything larger is rejected outright, so large files have to go through an upload URL or be sent in pieces.

4. You get 405 Method Not Allowed

   The Method the caller uses does not match the Webhook node's setting — they POST while your node is set to GET, or the other way around. Open the node panel and set both sides to the same Method. Sometimes the outside service defaults to GET while you assumed POST, so test it by hand once with curl or Postman.

5. The caller keeps retrying the same request (the same record is processed many times)

   The caller (Stripe / LINE / GitHub) retries when it does not get a 200 in time. The usual cause is that you picked Response = When last node finishes and the workflow runs past their timeout (LINE is 3 seconds, Stripe is 3 seconds, GitHub is 10 seconds). The fix: switch to Response = Immediately so n8n answers 200 instantly and the processing runs in the background.

6. Calls come in too fast, n8n rejects them, Executions queue up

   An n8n instance has a concurrency limit — too many calls in a short window and requests jam up or get rejected outright. The fixes: (a) turn on Queue Mode (Appendix B) and add workers; (b) pair it with Split In Batches or a Wait node to stagger the work; (c) split "receive and store" from "process afterwards" into two workflows, where the first only writes and answers fast, and the second reads on a schedule.

7. Auth is on but the caller keeps getting 401

   They typed the header name or the value wrong — it is case sensitive, and a stray space or a quote around the value makes it fail. Use curl by hand to send the same header they send and test it once; and the header name in their docs has to line up with the field name in the n8n Header Auth node. It can also be the wrong Authentication type (Basic vs Header).

8. Executions shows no record of the webhook firing

   The Executions tab shows only recent successful runs by default — the filter at the top has Include failed, and you have to turn it on to see the failures. Beyond that, turn on Save Execution Progress in the workflow Settings to see the detail of each node. While you are building, set all three of Save Manual / Save Failed / Save Successful to Save.

Wrapping up: 22 chapters done — now it is your turn

You have worked through the whole Woow n8n Onboarding Guide. From Chapter 1, "What n8n is", to Chapter 22, "Webhook", this learning path took you from "I have heard of Zapier" to "I can wire up a LINE bot myself and give a workflow a brain that thinks". Here is what you can do now:

• Create a new workflow yourself, drop nodes in, and chain Trigger + Action + Core (Chapters 7–10).
• Integrate the SaaS your company uses most — Slack, Gmail, Google Sheets, Drive, any service with an API (Chapters 11–13).
• Write expressions to grab upstream data, branch with IF/Switch, and handle many items with Merge/Split (Chapters 14–16).
• Handle errors, reshape data, pull reusable logic into a sub-workflow, and write a few lines of Code as an escape hatch (Chapters 17–20).
• Give a workflow AI judgment, and receive webhooks from outside (Chapters 21–22).

The rest is doing it. Honest advice: find one thing your company has done over and over in the past three months — tidying a report by hand every morning, sending a reminder email every week, replying to every LINE customer with the same canned message — and open a workflow that kills it off. The moment your first workflow goes live you will realize: "so this really does not need a person at all." And then you will not be able to stop.

When you get stuck along the way:

• You forgot how to configure a node → go back to the matching chapter (the contents list them all at the start).
• A node with a red border that does not run → see Appendix B · Error troubleshooting.
• You cannot find a setting → see Appendix A · Settings reference.
• You want to go deeper on self-hosting → see Appendix C · How it works underneath.

May your workflows all run smoothly, may they go live without incident, and may your boss give you a raise when the automation lands. You can always come back to a chapter, or ask the official n8n community at community.n8n.io — plenty of people are walking the same road.

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