Go

Installation

Install the package

go get github.com/KeplarsHQ/go-sdk

Set your API key

export KEPLARS_API_KEY=kms_your_workspace_id.live_your_secret

Send your first email

package main

import (
    "context"
    "fmt"
    "os"

    "github.com/KeplarsHQ/go-sdk/keplars"
)

func main() {
    client, err := keplars.NewClient(os.Getenv("KEPLARS_API_KEY"))
    if err != nil {
        panic(err)
    }

    ctx := context.Background()
    response, err := client.Emails.SendInstant(ctx, &keplars.SendEmailRequest{
        From:    "[email protected]",
        To:      "[email protected]",
        Subject: "Hello!",
        Body:    "<h1>It works!</h1>",
        IsHTML:  true,
    })
    if err != nil {
        panic(err)
    }

    fmt.Println("ID:", response.ID)
}

Priority Levels

Method	Delivery	Use case
`SendInstant`	0–5 seconds	OTP, 2FA, password reset
`SendHigh`	0–30 seconds	Transactional confirmations
`SendAsync` / `Send`	0–5 minutes	Welcome emails, notifications
`SendBulk`	Background	Newsletters, campaigns

client.Emails.SendInstant(ctx, req)
client.Emails.SendHigh(ctx, req)
client.Emails.SendAsync(ctx, req)
client.Emails.SendBulk(ctx, req)

Using Templates

response, err := client.Emails.SendInstant(ctx, &keplars.SendEmailRequest{
    From:       "[email protected]",
    To:         "[email protected]",
    TemplateID: "your-template-id",
    Params: map[string]interface{}{
        "user_name":         "Jane",
        "verification_code": "123456",
    },
})

Schedule an Email

response, err := client.Emails.Schedule(ctx, &keplars.ScheduleEmailRequest{
    From:         "[email protected]",
    To:           "[email protected]",
    Subject:      "Weekly digest",
    Body:         "<p>Here is your digest.</p>",
    IsHTML:       true,
    ScheduledFor: "2026-02-01T09:00:00Z",
    Timezone:     "America/New_York",
})

Error Handling

import "github.com/KeplarsHQ/go-sdk/keplars"

response, err := client.Emails.SendInstant(ctx, req)
if err != nil {
    var authErr *keplars.AuthenticationError
    var rateLimitErr *keplars.RateLimitError
    switch {
    case errors.As(err, &authErr):
        fmt.Println("Invalid API key")
    case errors.As(err, &rateLimitErr):
        fmt.Printf("Rate limit hit, retry after: %v\n", rateLimitErr.RetryAfter)
    default:
        panic(err)
    }
}

Admin API

Need to manage contacts, audiences, automations, or domains? Use an admin key - same client, different key suffix:

client, _ := keplars.NewClient("kms_xxx.adm_xxx")

client.Contacts.Add(ctx, &keplars.AddContactRequest{Email: "[email protected]", Name: "Jane"})
client.Audiences.Create(ctx, "Newsletter", "")
client.Automations.Enroll(ctx, "auto_id", "[email protected]")
client.Domains.Verify(ctx, "domain_id")

See the full Admin API reference.

Next Steps

Admin API - Contacts, audiences, automations, domains
Send Emails - API reference
Email Templates - Build reusable templates
Schedule Emails - Delayed delivery

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