Subject Line Performances (Coming Soon)

GET

/api/v3/letters/subject-line-performances

This endpoint returns the top 5 and bottom 5 performing subject lines for the authenticated company, ranked by open rate. As a v3 endpoint, it requires a company-derived API key.

It returns two arrays — top and bottom — each containing up to 5 items with the subject line text, open rate percentage, send count, and associated newsletters, channels, and organizations.

No analysis is included; this is purely metrics-driven.

Authorizations

• bearerAuth

Parameters

Query Parameters

api

string

Example

true

required | When set to true, this endpoint will accept authorization with your API Key.

Responses

200

Subject Line Performances (Coming Soon)

Media type application/json

object

items

object

bottom

Array<object>

object

channel

string

letter

string

openRate

number

organization

string

sent

number

subject

string

top

Array<object>

object

channel

string

letter

string

openRate

number

organization

string

sent

number

subject

string

message

string

total

number

Examples

Example Subject Line Performances (Coming Soon)

{
  "items": {
    "bottom": [
      {
        "channel": "black-bitter-tea",
        "letter": "dtqw2gzyqu",
        "openRate": 0,
        "organization": "black-bitter-coffee-brand",
        "sent": 0,
        "subject": "Anna's Cupcake Shop"
      },
      {
        "channel": "black-bitter-coffee",
        "letter": "17nsgad7m9",
        "openRate": 0,
        "organization": "black-bitter-coffee-brand",
        "sent": 0,
        "subject": "F1 Unlocked Template"
      },
      {
        "channel": "black-bitter-coffee",
        "letter": "n3wdcbv4bs",
        "openRate": 0,
        "organization": "black-bitter-coffee-brand",
        "sent": 3,
        "subject": "A New Right Quick"
      },
      {
        "channel": "black-bitter-coffee",
        "letter": "4f3fsndi0s",
        "openRate": 0,
        "organization": "black-bitter-coffee-brand",
        "sent": 3,
        "subject": "Create and Monetize Great Newsletters Easily"
      },
      {
        "channel": "black-bitter-coffee",
        "letter": "5gr5nkngrf",
        "openRate": 0,
        "organization": "black-bitter-coffee-brand",
        "sent": 0,
        "subject": "F1 Unlocked Template"
      }
    ],
    "top": [
      {
        "channel": "black-bitter-iced-tea-times",
        "letter": "vkky0g63zs",
        "openRate": 100,
        "organization": "black-bitter-coffee-brand",
        "sent": 1,
        "subject": "Draft 720"
      },
      {
        "channel": "black-bitter-coffee",
        "letter": "nrhi21smx3",
        "openRate": 100,
        "organization": "black-bitter-coffee-brand",
        "sent": 13,
        "subject": "F1 Unlocked Template"
      },
      {
        "channel": "black-bitter-coffee",
        "letter": "0xlfgg8owg",
        "openRate": 100,
        "organization": "black-bitter-coffee-brand",
        "sent": 1,
        "subject": "Harsh E2E Test"
      },
      {
        "channel": "black-bitter-coffee",
        "letter": "ndefdg8zl0",
        "openRate": 92,
        "organization": "black-bitter-coffee-brand",
        "sent": 13,
        "subject": "F1 Unlocked Template"
      },
      {
        "channel": "black-bitter-coffee",
        "letter": "2tebekvmiu",
        "openRate": 92,
        "organization": "black-bitter-coffee-brand",
        "sent": 13,
        "subject": "F1 Unlocked Template"
      }
    ]
  },
  "message": "Do something kind today",
  "total": 10
}

Headers

Alt-Svc

string

Example

h3=":443"; ma=2592000,h3-29=":443"; ma=2592000

Transfer-Encoding

string

Example

chunked

access-control-allow-credentials

string

Example

true

access-control-allow-origin

string

Example

*

access-control-max-age

string

Example

86400

cache-control

string

Example

no-cache, private

date

string

Example

Wed, 18 Mar 2026 23:06:01 GMT

server

string

Example

nginx/1.27.3

via

string

Example

1.1 google

x-powered-by

string

Example

PHP/7.4.33