Text formatting

Chert includes native text formatting for iMessage. Send plain text in value and describe styles with text_decorations; Markdown asterisks remain literal.

Formatting is an existing line-enabled preview. Confirm access with Chert before using it. The initial scope is one text part in an existing phone-addressed iMessage direct chat. Group messages, replies, attachments, SMS/RCS, and animated text effects are outside this preview. Other lines can reject decorated requests with code 4099; do not assume every Chert API host or SDK accepts them.

Send formatted text

Use POST /api/v1/chats/{chat_id}/messages on the enabled line. Save this body as formatted-message.json and use a stable idempotency key for this operation:

{
  "message": {
    "idempotency_key": "format-four-styles-001",
    "parts": [{
      "type": "text",
      "value": "Bold Italic Underline Strike",
      "text_decorations": [
        { "range": [0, 4], "style": "bold" },
        { "range": [5, 11], "style": "italic" },
        { "range": [12, 21], "style": "underline" },
        { "range": [22, 28], "style": "strikethrough" }
      ]
    }]
  }
}

curl "https://console.trychert.com/api/v1/chats/$CHAT_ID/messages" \
  -H "Authorization: Bearer $CHERT_SIGNING_SECRET" \
  -H "Content-Type: application/json" \
  --data-binary @formatted-message.json

import { readFile } from "node:fs/promises";
const response = await fetch(
  `https://console.trychert.com/api/v1/chats/${process.env.CHAT_ID}/messages`,
  {
    method: "POST",
    headers: {
      Authorization: `Bearer ${process.env.CHERT_SIGNING_SECRET}`,
      "Content-Type": "application/json"
    },
    body: await readFile("formatted-message.json", "utf8")
  }
);
const result = await response.json();
// Inspect response.status and result; acceptance is not delivery.

import os, requests
with open("formatted-message.json", "rb") as body:
    response = requests.post(
        f"https://console.trychert.com/api/v1/chats/{os.environ['CHAT_ID']}/messages",
        headers={
            "Authorization": f"Bearer {os.environ['CHERT_SIGNING_SECRET']}",
            "Content-Type": "application/json",
        },
        data=body.read(),
        timeout=30,
    )
result = response.json()  # Inspect status_code; acceptance is not delivery.

Range rules

range is [start, end): zero-based UTF-16 code units, with an exclusive end.
Supported styles are bold, italic, underline, and strikethrough.
Ranges must be nonempty, inside value, and must not split a surrogate pair. JavaScript string offsets use UTF-16; Python character offsets need conversion when the text contains characters outside the Basic Multilingual Plane.
Different styles can overlap. Equivalent adjacent/overlapping ranges of the same style are combined. At most 256 input decorations are accepted.
Preserve the exact text used to calculate offsets. This path does not trim or normalize the text before applying styles.

Acceptance, status, and inbound formatting

A new accepted request returns HTTP 202 with a message object containing id, chat_id, the decorated parts, and status: "queued". Save message.id and use GET /api/v1/messages/{id} to inspect recorded status. Neither a queued receipt nor a delivery status proves the recipient rendered each style. Reuse the same key and identical text/styles when reconciling the original operation. Changing the request under that key conflicts. An unconfirmed result with retryable: false must not trigger another send or a new key. On enabled lines, message.received.data.message.parts[] and recorded chat history can contain the same text_decorations shape. Keep value as readable plain text when your client cannot render styles. Missing decorations do not establish that the sender used no formatting.

Failure	What to do
Invalid style/range (`1002`)	Correct the request before creating a new operation.
Unsupported line or chat (`4099`)	Confirm preview access and use an eligible existing direct chat.
Conflicting idempotency key (HTTP `409`)	Reconcile the original operation; do not reuse its key for different content.
Unconfirmed outcome (`4103`, `retryable: false`)	Inspect recorded status and contact Chert before sending again.

See Send a message and Receiving replies.

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Messages

Chats

Group chats

Contact sharing

Webhooks and events

Reference

Text formatting

Send formatted text

Range rules

Acceptance, status, and inbound formatting

​Send formatted text

​Range rules

​Acceptance, status, and inbound formatting

Send formatted text

Range rules

Acceptance, status, and inbound formatting