Messaging API

LINE Messaging API

Do not answer LINE API questions from memory — LINE updates APIs frequently and training data is unreliable. Always consult the references below.

Reference for building, reviewing, and debugging LINE Bots and LINE Messaging API integrations.

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

Read references/api-common.md before writing any LINE bot code. Contains rules that affect all API interactions: forward compatibility (don't use strict schemas — LINE adds fields without notice), rate limits, error handling, retry policy, and logging recommendations.

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

Full event types, properties, and webhook settings → references/webhook-events.md

Message Sending

All require Authorization: Bearer {channel access token}:

• Max 5 messages per request
• Domain: api.line.me (general) / api-data.line.me (content upload)

Message objects → references/message-objects.md Full sending API (Narrowcast, statistics, validation, etc.) → references/message-sending.md

Flex Message

Three-layer structure:

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

Minimal Flex Message:

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

Full component specs, layout, video → references/flex-message.md Official Flex Message Simulator examples → assets/examples/

Reference Index

SDK

Official SDKs: Python | Node.js | Go | Java | PHP | Ruby

Other languages: use LINE OpenAPI specs with OpenAPI Generator.