LINE Messaging API

Workflow

Build

1. Read references/api-common.md (rate limits, forward compatibility, error handling)
2. Load the relevant reference for the feature being implemented
3. For architecture or design choices, consult references/experts.md for directional guidance
4. Write code following specs and constraints from references

Review / Debug

1. Read references/api-common.md (rate limits, error codes)
2. Load relevant references for the code being reviewed
3. Cross-check code against specs (size limits, token expiry, counting rules, required fields)
4. For design pattern concerns, consult references/experts.md
5. Report violations with reference to specific constraints

Environment Variables

LINE_CHANNEL_ACCESS_TOKEN=Bot access token
LINE_CHANNEL_SECRET=Channel secret (webhook signature verification)

Common Specifications

Webhook

• Verification:

  x-line-signature

  header (HMAC-SHA256, base64, key = Channel Secret)
• Body:

  {"destination": "U...", "events": [...]}

• Bot server must return

  200

Signature Verification (pseudocode)

channel_secret = ENV['LINE_CHANNEL_SECRET']
signature = request.headers['x-line-signature']
body = request.body   # raw bytes, do NOT parse/reformat before verification

digest = HMAC_SHA256(key = channel_secret, message = body)
expected = Base64.encode(digest)

if signature != expected:
    return 403  # reject — not from LINE

events = JSON.parse(body)['events']
for event in events:
    handle(event)
return 200

• Never deserialize or re-format the body before verification
• Use UTF-8 encoding exclusively
• Official SDKs handle this automatically — use them when possible

Message Sending

Authorization: Bearer {channel access token}

POST /v2/bot/message/reply

POST /v2/bot/message/push

POST /v2/bot/message/multicast

POST /v2/bot/message/broadcast

• Max 5 messages per request
• Domain:

  api.line.me

  (general) /

  api-data.line.me

  (content upload)

Flex Message

Container (Bubble / Carousel)
  └── Block (Header / Hero / Body / Footer)
       └── Component (Box / Button / Image / Video / Icon / Text / Span / Separator)

{
  "type": "flex", "altText": "Notification",
  "contents": {
    "type": "bubble",
    "body": {
      "type": "box", "layout": "vertical",
      "contents": [{"type": "text", "text": "Hello Flex!", "weight": "bold"}]
    }
  }
}

assets/examples/

Reference Index

SDK