A2P Messaging API
AI & MCP
Build with the A2P Messaging API from your AI assistant: this zone's docs as plain markdown, one autocontained dump, the OpenAPI specs and a drop-in prompt. The Messaging MCP, an MCP server for the A2P Messaging API, is coming soon.
Everything in this zone is published for machines as well as people: every page as plain markdown, the whole API as one file you can paste into an assistant, and the contracts as OpenAPI. That is how you build with the A2P Messaging API from your AI tools today. An MCP server of its own is on the way.
Messaging MCP Coming soon
The Messaging MCP, an MCP server for the A2P Messaging API, is coming soon. Until it ships, point your assistant at the artefacts below: with the dump and the spec in context, it writes and reviews integration code against the current API instead of guessing from its training data.
What's available
Every page of this API in one autocontained markdown file: quickstart, bulk sending, authentication, rate limits, errors, DLRs, SMPP and the SDKs. The one file to paste.
llms.txt — this zone's indexThe table of contents of the A2P Messaging API docs, one line per page, following the llmstxt.org convention. Fits in any context window.
OpenAPI specThe API contract as YAML. Import it into Postman, generate a typed client, or give it to an assistant for exact request and response shapes.
Per-page markdownEvery page has a .md twin at the same URL plus .md, for an agent that fetches one page at a time.
Still on the Legacy API? It has its own dump, /a2p-messaging-api/legacy/llms-full.txt, and spec, /openapi/legacy.openapi.yaml — useful for an assistant that is helping you migrate.
Drop-in prompt
Paste this into your agent's rules file — CLAUDE.md for Claude Code, .cursorrules for Cursor, .windsurfrules for Windsurf — or as the first message of a chat. It tells the assistant what the API is, where its docs are and how to fetch them.
# Instasent A2P Messaging API — integration context
The A2P Messaging API sends messages from your code over HTTP (REST) or
SMPP: SMS today, RCS and WhatsApp coming soon. Also known as the
Transactional API and, formerly, the SMS API: three names for the same
API, which is why the URLs say "transactional".
Base URL: https://api.instasent.com/transactional/v1
- Single send: POST /sms (OTPs, receipts, alerts).
- Bulk send: POST /sms/bulk, up to 100 messages per request. Accepted
messages are queued and drained at carrier speed, so one bulk call
outperforms many parallel single sends.
- Delivery reports (DLRs) pushed to your webhook; HLR / number lookup;
balance and price profiles.
- SDKs: Node.js, PHP, Python, Ruby, Java.
- Authentication: Bearer token in the Authorization header; SMPP binds
with system_id / password.
Docs (fetch before writing or reviewing code that calls the API):
https://staging-instasent-docs-nextjs.oscar-284.workers.dev/a2p-messaging-api/llms-full.txt
OpenAPI spec:
https://staging-instasent-docs-nextjs.oscar-284.workers.dev/openapi/transactional.openapi.yaml
Any page as markdown: its URL plus ".md". Index of this zone:
https://staging-instasent-docs-nextjs.oscar-284.workers.dev/a2p-messaging-api/llms.txt
Instasent's other product, the Platform — a CDP for mass marketing, with
its own API — is documented separately at
https://staging-instasent-docs-nextjs.oscar-284.workers.dev/platform-api/llms.txt — use it only if the job needs
Instasent to hold the audience.
Per-page markdown
Every page of this zone has a markdown twin at the same URL plus a .md suffix, built from the same source as the HTML, so the two never drift.
/a2p-messaging-api/http/quickstart → /a2p-messaging-api/http/quickstart.md
/a2p-messaging-api/http/dlrs → /a2p-messaging-api/http/dlrs.md
/a2p-messaging-api/smpp/integration → /a2p-messaging-api/smpp/integration.md
Every page also carries Copy and Ask AI next to its title: the first copies that page's markdown, the second opens your assistant with a prompt that already points at this API's dump.
Paste into a chat
Grab the dump
Download
llms-full.txt, or copy its URL if your assistant can fetch.Attach it
Attach the file to the conversation, or paste its contents.
Ask in context
"Here are the Instasent A2P Messaging API docs. Write a Node.js function that sends a bulk SMS and handles the DLR webhook." The answer is grounded in the current API.