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Klaviyo

Klaviyo API

Yes. Klaviyo publishes a public REST API with OAuth with dynamic client registration; requires an Owner, Admin or Manager role auth. See developers.klaviyo.com/en/docs/klaviyo_mcp_server for the full reference.

Auth: OAuth with dynamic client registration; requires an Owner, Admin or Manager roleMCP also available
Open API docsTry Klaviyo
Public REST API documentedAgent-readiness 7/10
Facts verified 2026-08-06

What is the Klaviyo API?

The Klaviyo API is a public REST interface to campaigns, contacts, segments, and automation workflows. Auth method is documented on the official API reference. No official SDK was detected, so most teams hit it directly with HTTP clients.

Typical builds: scripts that sync subscribers from your product database, engagement dashboards that combine open rate with revenue attribution, and cron jobs that pause underperforming campaigns automatically.

For agent workflows specifically, the official MCP server is usually less code than the REST API. The API still wins for scheduled jobs, dashboards, and anything outside an LLM-driven flow.

For the broader picture: Klaviyo review, full pricing breakdown, .

HOOK IT TO YOUR STACK

Real Klaviyo API calls you'll write

klaviyo-apirest
#List campaigns from the last 30 days
GET/v3/campaigns?since=30d&fields=name,open_rate,clicks
200 OK · 12 campaigns
Black Friday Teaseropen 42.1%
Product launchopen 38.5%
Weekly digest #12open 27.0%
Welcome flow step 2open 61.3%
klaviyo-apirest
#Create a new automation programmatically
POST/v3/automations
201 Created · automation_id: aut_8x
Statusdraft
Steps configured0
Estimated audience2,847
Push steps via PUT /automations/{id}/steps.
klaviyo-apirest
#Add a contact and tag them in one call
POST/v3/contacts
201 Created · contact_id: c_4f12
Lifecycle stagesubscriber
Tags applied1
Triggers firedwelcome-series
TMB SCORE FOR KlaviyoAgent fit: 7/10
Read review →

Endpoints illustrative. Confirm exact paths against the live API docs before integrating.

How much does the Klaviyo API actually cost?

Usage-based

Klaviyo's API is included with every paid plan, but SMS, MMS, and WhatsApp are billed per message.

  • Email API access is included with the same plan that powers the dashboard, pricing scales by active profiles.
  • SMS, MMS, RCS, and WhatsApp are usage-based: you pay per send (varies by destination country).
  • Heavy programmatic senders should budget separately for the usage layer on top of the base subscription.

API at a glance

Auth method
OAuth with dynamic client registration; requires an Owner, Admin or Manager role
SDK languages
—
OpenAPI spec
—
Webhooks
—
Structured outputs
—

Klaviyo also has an MCP server

If you're wiring Klaviyo into Claude / Cursor / Codex, the MCP server is usually less code than the REST API.

See Klaviyo MCP page

What you can build with the Klaviyo API

Three personas, three different shapes of build. Pick the row that matches how you actually ship.

SOLO DEV / FOUNDER

Glue Klaviyo into your daily workflow

  • Pull a digest of campaign performance into your morning Slack
  • Trigger a one-off backfill when something looks off
  • Pipe data into your own SQLite for ad-hoc queries
Effort: A weekend, one Node or Python script
AGENCY / CONSULTANT

Sell Klaviyo reporting at scale

  • White-label Klaviyo data into client-branded dashboards
  • Run scheduled multi-account reports without logging into the Klaviyo UI
  • Cross-reference with the rest of the client's stack (CRM, analytics, ad spend)
Effort: 1-2 weeks, hits multi-tenant auth quickly
IN-HOUSE ENGINEER

Production pipelines for Klaviyo

  • Real-time sync into your warehouse on a cron
  • Custom alerts the dashboard's built-in alerting can't express
  • Backfill + idempotency handling for Klaviyo data older than the dashboard exposes
Effort: Multi-week project, expect rate-limit tuning

Quickstart template

# Starter template — endpoint paths and SDK package names come from
# the Klaviyo API docs: https://developers.klaviyo.com/en/docs/klaviyo_mcp_server

curl -X GET "https://developers.klaviyo.com/<your-endpoint>" \
  -H "Authorization: Bearer $TOKEN" \
  -H "Accept: application/json" | jq .

Template only. Endpoint paths, exact base URL, and auth header format come from developers.klaviyo.com/en/docs/klaviyo_mcp_server.

Limits and gotchas

  • No OpenAPI spec — you write typed clients by hand or use a third-party generator on the docs HTML.
  • No official SDK detected. Plan on hitting the API directly with your HTTP client of choice.
  • Rate limits: always read the docs page before scaling — the published limit is usually lower than the practical one and overages can be expensive.
  • No-code fallback: Zapier and Make.com cover the common triggers if you want to skip writing API code for simple flows.
7/10

Agent-readiness verdict

Good agent fit with official MCP support. Klaviyo offers an official MCP server and documented public API with native Claude and ChatGPT integration, making it straightforward to add to agentic workflows. The missing OpenAPI spec and lack of webhooks limit some automation patterns, but the MCP availability handles most agent use cases.

Klaviyo API FAQ

Does Klaviyo have a public API?+
Yes — REST API at developers.klaviyo.com/en/docs/klaviyo_mcp_server.
Should I use the API or the MCP server for Claude / Cursor / Codex?+
Prefer the MCP server for agent workflows — it's less code and pre-handles auth flows. Use the REST API for scheduled jobs, dashboards, and anything outside an LLM-driven flow.

Sources

Joonas Rotko
Joonas RotkoAuthor & Founder of That Marketing Buddy

10+ years in digital marketing. I review marketing software for AI-stack fit: real pricing, MCP and API support, and how cleanly each tool drops into an AI agent workflow, cross-checked against verified data and real user feedback.

About meHow I review

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