Quickstart · Dashboard · Metrics · Alerting · Deployment

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Your transactional email fails silently: the appointment confirmation bounces, the password reset never arrives, and you find out from a support ticket three days later. Resend knows the moment it happens — resend-exporter turns that moment into a Prometheus alert.

It receives Resend webhook events, verifies their Svix signatures, and exposes clean Prometheus metrics — so the monitoring stack you already run pages you when email breaks.

Why this exists

• Alert on what matters — a bounced confirmation email is an incident, not a dashboard curiosity. increase(resend_email_events_total{event_type="email.failed"}[5m]) > 0 and you're paged.
• Metrics stay clean, logs stay detailed — counters answer "how many & how bad", structured JSON logs answer "which email & why". Recipient addresses and subjects are redacted or hashed by default, so metrics and dashboards are safe to share.
• Cardinality-safe by construction — recipient domains are bucketed (well-known providers keep their name, the long tail becomes other), so one busy tenant can't blow up your Prometheus.
• Boring to operate — a single compiled binary in a distroless image, three runtime dependencies, no database, no Resend API key needed.

How it works

flowchart LR
    R[Resend] -->|"Svix-signed webhooks"| E["resend-exporter<br/>verify · count · log"]
    E -->|"/metrics"| P[Prometheus]
    P --> G["Grafana<br/>dashboards + alerts"]
    E -.->|"JSON logs"| L[(Loki / stdout)]

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Method	Path	Purpose
POST	/webhooks/resend	Receive Resend webhook events
GET	/metrics	Prometheus metrics
GET	/healthz	Liveness probe
GET	/readyz	Readiness probe

Quickstart

Docker

docker run -p 8080:8080 \
  -e RESEND_WEBHOOK_SECRET=whsec_... \
  ghcr.io/robbeverhelst/resend-exporter:latest

Helm

helm install resend-exporter oci://ghcr.io/robbeverhelst/charts/resend-exporter \
  --set resend.webhookSecret=whsec_... \
  --set serviceMonitor.enabled=true

Local playground — exporter + Prometheus (alert rules loaded) + Grafana (dashboard provisioned):

docker compose up --build

Then point a Resend webhook at https://your-host/webhooks/resend (dashboard → Webhooks → Add, copy the whsec_ signing secret) and scrape /metrics. The webhook path needs to be internet-reachable; /metrics should not be. Details in docs/deployment.md.

The dashboard

Ships in examples/grafana/dashboards/ — import it, or let the compose playground / your dashboard sidecar provision it:

Metrics

resend_webhook_events_total{event_type="email.bounced",domain="acme.dev"}
resend_email_events_total{event_type="email.bounced",from_domain="acme.dev",to_domain="outlook.com"}
resend_webhook_signature_failures_total
resend_webhook_handler_errors_total{reason="invalid_json"}
resend_webhook_last_event_timestamp_seconds{event_type="email.delivered"}

Full reference and the cardinality design: docs/metrics.md. Ready-made alert rules (any failure, bounces, repeated delays, signature failures, stale webhook): docs/alerting.md and examples/prometheus/alerts.yml.

Configuration

Variable	Required	Default	Description
RESEND_WEBHOOK_SECRET	yes	—	Svix signing secret (whsec_...) from the Resend webhook settings
RESEND_EXPORTER_ADDR	no	:8080	Listen address (host:port or :port)
RESEND_EXPORTER_WEBHOOK_PATH	no	/webhooks/resend	Webhook path
RESEND_EXPORTER_METRICS_PATH	no	/metrics	Metrics path
RESEND_EXPORTER_LOG_LEVEL	no	info	debug, info, warn, error
RESEND_EXPORTER_REDACTION_MODE	no	strict	strict, hash, or none — see docs/configuration.md
RESEND_EXPORTER_TO_DOMAIN_ALLOWLIST	no	—	Extra recipient domains kept as their own to_domain label value
RESEND_EXPORTER_SERIES_HOLD_SECONDS	no	60	New-series hold window; set >= your longest scrape interval

Documentation

• Configuration — every environment variable, redaction modes
• Metrics — metric reference and cardinality design
• Alerting — PromQL alert examples for Grafana/Alertmanager
• Deployment — Docker, Helm, docker-compose, exposing the webhook
• Development — building, testing, and the release process

Stability

resend-exporter follows semver. As of 1.0.0, the following are stable interfaces — breaking changes to any of them mean a major release:

• Configuration environment variables and their semantics
• Metric names, types, and label sets
• HTTP endpoints and their behavior (paths themselves are configurable)
• Helm chart values
• The structured log schema (field names; redaction guarantees)

Roadmap

• Optional Resend API reconciliation: backfill missed events after downtime, verify webhook configuration, and enrich sparse events (RESEND_API_KEY is already reserved for this)
• Delivery-delay histogram and bounce-type breakdown metrics

Non-goals: replacing the Resend dashboard, storing email content, and sending alert notifications directly — routing belongs in Grafana Alerting, Alertmanager, ntfy, Slack, or PagerDuty.

Contributing

PRs welcome — see CONTRIBUTING.md. The short version: bun install, bun test, conventional commits (every feat:/fix: on main ships a release automatically).

License

MIT