{"id":3067,"date":"2026-10-07T14:00:38","date_gmt":"2026-10-07T08:30:38","guid":{"rendered":"https:\/\/www.smsgatewaycenter.com\/blog\/?p=3067"},"modified":"2026-10-09T12:18:25","modified_gmt":"2026-10-09T06:48:25","slug":"two-way-sms-keyword-routing-auto-reply-design","status":"publish","type":"post","link":"https:\/\/www.smsgatewaycenter.com\/blog\/two-way-sms-keyword-routing-auto-reply-design\/","title":{"rendered":"Two-Way SMS Keyword Design: Routing, Auto-Replies and Conversation State on a Long Code"},"content":{"rendered":"\n

<\/a><\/p>\n\n\n\n

A customer texts “ACME BAL” to your long code. What happens next is your code’s job: matching the keyword, remembering where the conversation was, sending a reply that passes DLT, and not answering the same message twice. This guide shows how to build that router on SMSGatewayCenter<\/strong>‘s long code push<\/a>, with working samples in Python, Node.js, Java and PHP.<\/p>\n\n\n\n

\"Abstract<\/a>
Every inbound text goes through one router. What it decides determines which reply goes back.<\/figcaption><\/figure>\n\n\n\n

Table of Contents<\/h1>\n\n\n\n
    \n
  1. The Short Answer<\/a><\/li>\n\n\n\n
  2. TL;DR<\/a><\/li>\n\n\n\n
  3. What Happens When Someone Texts Your Long Code<\/a><\/li>\n\n\n\n
  4. Shared or Dedicated: Who Owns the First Word<\/a><\/li>\n\n\n\n
  5. The Callback Template Is Yours to Shape<\/a><\/li>\n\n\n\n
  6. Designing the Keyword Namespace<\/a><\/li>\n\n\n\n
  7. Normalising What People Actually Type<\/a><\/li>\n\n\n\n
  8. The Router: From Raw Text to an Intent<\/a><\/li>\n\n\n\n
  9. Conversation State That Survives Real Traffic<\/a><\/li>\n\n\n\n
  10. Auto-Replies Are Outbound SMS, With All the Rules<\/a><\/li>\n\n\n\n
  11. Portal Reply or Your Own Reply: Pick One Owner<\/a><\/li>\n\n\n\n
  12. Deduplicating a Push With No Message ID<\/a><\/li>\n\n\n\n
  13. Stopping Reply Loops and Reply Storms<\/a><\/li>\n\n\n\n
  14. Keeping Replies Fast While a Campaign Is Sending<\/a><\/li>\n\n\n\n
  15. Locking Down the Callback URL<\/a><\/li>\n\n\n\n
  16. Four Code Samples, Four Traps<\/a><\/li>\n\n\n\n
  17. Testing a Keyword Flow Before Launch<\/a><\/li>\n\n\n\n
  18. Decision Matrix<\/a><\/li>\n\n\n\n
  19. Launch Checklist<\/a><\/li>\n\n\n\n
  20. Unspecified Behaviour and How to Code Around It<\/a><\/li>\n\n\n\n
  21. FAQs<\/a><\/li>\n<\/ol>\n\n\n\n

    The Short Answer<\/h2>\n\n\n\n

    On SMSGatewayCenter<\/strong>, the platform does one job for you when someone texts your long code: it matches the approved keyword and forwards the message to your URL as an HTTP GET. Everything after that is yours. Your code decides what the text means, remembers where that person is in a conversation, picks a reply, and sends it back through SMSApi\/send<\/code> like any other outbound SMS, which means a registered sender ID and a DLT-approved template.<\/p>\n\n\n\n

    So build it as four small pieces. An endpoint that saves the raw message, dedupes it and answers 200 straight away. A router that normalises the text and maps it to an intent. A state table, one row per phone number and long code, with a version column so two quick texts can’t trample each other. And a reply sender with a budget per number, so a misbehaving auto-responder on the other end can’t drag you into a loop.<\/p>\n\n\n\n

    Two decisions matter more than the code. First, decide who owns the reply: the portal’s Default Response or your webhook, never both, or people get two answers. Second, design your keywords as a namespace: one approved primary keyword that the platform routes on, and your own sub-commands after it (ACME BAL<\/code>, ACME HELP<\/code>), which you can change any day without waiting for approval.<\/p>\n\n\n\n

    TL;DR<\/h2>\n\n\n\n
    Question<\/th>Answer<\/th><\/tr><\/thead>
    What does the platform do with an inbound text?<\/td>Matches the approved keyword on the long code and forwards the message to your Callback URL (HTTP GET). It can also send one fixed Default Response and copy the message to an SMS number, an email address or Telegram.<\/td><\/tr>
    What’s in the forwarded request?<\/td>Whatever your callback template says. The placeholders are $vmn<\/code>, $location<\/code>, $mobile<\/code>, $message<\/code>, $operator<\/code>, $timestamp<\/code> and $keyword<\/code>. The parameter names are yours to choose.<\/td><\/tr>
    Is there a message ID?<\/td>No. Build your own dedupe key from the long code, the sender’s number, $timestamp<\/code> if you include it, and the normalised text.<\/td><\/tr>
    Shared or dedicated long code?<\/td>On a shared code, the primary keyword is what separates your traffic from everyone else’s. On a dedicated code, every text to the number is yours and you get unlimited keywords.<\/td><\/tr>
    How should you name keywords?<\/td>One short approved primary keyword, then your own sub-commands after it. Keep the sub-commands in your router so you can change them without re-approval.<\/td><\/tr>
    Can an auto-reply say anything?<\/td>No. It’s an outbound SMS, so in India it needs an approved sender ID and a DLT template. Build a reply catalogue that maps each intent to a dltTemplateId<\/code>.<\/td><\/tr>
    Portal Default Response and a webhook reply together?<\/td>Pick one. With both switched on, the customer gets two replies.<\/td><\/tr>
    How do you stop reply loops?<\/td>Cap replies per number per hour, never auto-reply to your own long code or sender, and stop replying after a run of unrecognised messages.<\/td><\/tr>
    What about STOP?<\/td>Handle it in your router before anything else, and write it to your suppression table. The opt-out and suppression guide<\/a> covers that in depth.<\/td><\/tr>
    How do you test without spamming real people?<\/td>Replay captured callback URLs against a staging endpoint and use a sandbox account<\/a> for the reply leg.<\/td><\/tr><\/tbody><\/table><\/div><\/figure>\n\n\n\n
    \n\n\n\n

    What Happens When Someone Texts Your Long Code<\/h2>\n\n\n\n

    It helps to picture the whole trip before writing any code, because each hop has a different owner and fails in a different way.<\/p>\n\n\n\n

    \"Three-panel<\/a>
    Three hops from a customer’s text to your reply. The platform owns the first; you own the other two.<\/figcaption><\/figure>\n\n\n\n

    Hop one: operator to platform.<\/strong> The customer sends a text to your 10-digit long code (also called a VMN, a virtual mobile number). The platform receives it and checks it against the keywords you’ve set up on that number. Keywords are created in the portal under Incoming SMS, 2 Way SMS, Add 2 Way SMS Keyword, and each one goes to the SMSGatewayCenter team for moderation before it’s live. You also need Incoming SMS credits on the account for the keyword to be approved.<\/p>\n\n\n\n

    Hop two: platform to you.<\/strong> For a matched keyword, the platform can do up to five things, each switched on per keyword in that same form:<\/p>\n\n\n\n