# Plunk

**Canonical:** https://apis.io/providers/plunk/  
**Website:** https://www.useplunk.com  
**APIs profiled:** 5

Plunk is an open-source (AGPL-3.0) email platform for developers that unifies transactional email, marketing campaigns, contact segmentation and event-driven workflow automation behind a single REST API. It publishes its own OpenAPI 3.1.0 at docs.useplunk.com/openapi.json, declaring next-api.useplunk.com as the production base URL, and authenticates with a two-class Bearer API key where the prefix decides capability — sk_ for every endpoint and pk_ for the client-safe /v1/track tracking call. The API supports Idempotency-Key on both public write endpoints, cursor pagination, a structured error envelope carrying machine codes plus remediation hints, and a documented webhook event catalogue delivered as workflow steps. Every documentation page is also served as Markdown. The entire stack self-hosts with Docker Compose for full data ownership and no per-email costs.

## Kin Score — 70.6 / 100 (exemplar)

Scored 2026-08-25 under rubric 0.14.0. Trend: flat (+0.0 from 70.6).

| Facet | Score |
|---|---|
| Discoverability | 81.5 |
| Contract Quality | 72.2 |
| Governance | 30.3 |
| Contract Governance | 30.3 |
| Operational Transparency | 73.7 |
| Developer Ergonomics | 63.7 |
| Commercial Clarity | 92.1 |
| Access Clarity | 92.1 |

## Agent readiness — 36.2 (agent-ready)

| Dimension | Value |
|---|---|
| Spec Presence | yes |
| Agentic Access | derived |
| Reversibility Documented | no |
| MCP Server | no |
| Auth Clarity | bearer |
| Idempotency | documented |
| Error Semantics | documented |
| OpenAPI Examples | verified |
| Rate Limit Signal | documented |
| Event Surface Described | yes |
| Agent Skills | derived |
| Well Known Catalog | no |
| Consent Identity | no |
| Agent Card | no |
| Dry Run Mode | no |
| Delegated Identity | no |
| Protected Resource Metadata | no |
| Dynamic Client Registration | no |
| Agentic Commerce | no |

## Access

Freemium · Open access — onboarding: open, pricing: freemium, trial: no (confidence: high).

## APIs (5)

- **Plunk API** — Plunk's own published OpenAPI 3.1.0, served at https://docs.useplunk.com/openapi.json and declaring https://next-api.useplunk.com as the production base URL. Covers the public A...
- **Plunk Campaigns API** — Create and send marketing campaigns.
- **Plunk Contacts API** — Manage contacts and their subscription state.
- **Plunk Events API** — Track contact events that drive automations.
- **Plunk Transactional API** — Send transactional email.

## Agentic access (1)

- **Plunk Agentic Access** — 14 operations · 11 acting

## Security (2)

- **Plunk Authentication** — http · 1 scheme
- **Plunk Domain Security** — TLSv1.3 · DMARC

## Plans (1)

- **Plunk Plans Pricing**

## Tags

Email, Transactional Email, Marketing, Automation, Open-Source, Software-as-a-Service, Email API, Webhook, Segmentation, Workflow-Automation, Self-Hosted, Developer Tools

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Profiled by [API Evangelist](https://apievangelist.com) and published on [APIs.io](https://apis.io/providers/plunk/). Scores are computed from the provider's own public artifacts under a published rubric.