Resend vs LangSmith

Resend

LangSmith

Resend · 12 features

• Audiences — Contact list management with custom fields.
• Batch Send — Send up to 100 emails in one API call.
• Broadcasts — Bulk email campaigns with audiences, A/B testing, analytics.
• Dedicated IP — Add-on for high-volume senders. Auto warmup.
• Domains — DKIM/SPF/DMARC auto-verification. Per-domain analytics.
• Idempotency — Prevent duplicate sends with Idempotency-Key header.
• Logs + Analytics — Full email logs, delivery heatmap, events table.
• React Email — OSS library (3M+ downloads) to compose emails in React/JSX.
• Scheduled Send — scheduledAt parameter for future delivery.
• Send API — POST /emails endpoint to send. Supports attachments, scheduled send, idempotency…
• Suppressions — Auto-managed bounce + complaint list. API to add/remove.
• Webhooks — Email lifecycle events: sent, delivered, bounced, complained, opened, clicked.

LangSmith · 14 features

• Alerts — Threshold alerts on latency, cost, eval metrics.
• Annotation Queues — Human-review workflows for trace quality rating.
• Custom Dashboards — Aggregate metrics dashboards per project/tag.
• Datasets — Collect examples → use as eval sets or training data.
• Evaluations — LLM-as-judge, embedding similarity, custom Python evaluators, offline batch eval…
• LangChain Integration — Auto-trace any LangChain/LangGraph run with env var.
• LangGraph Integration — First-class trace + eval for LangGraph agents.
• LLM Tracing — Automatic trace every LLM call + tool call + chain step.
• OpenTelemetry Export — Export traces as OTLP to Datadog/Honeycomb/etc.
• Playground — Test prompts + models inline before deploying.
• Prompt Canvas — Visual prompt editor with live test + eval.
• Prompt Hub — Public + private prompt library with versioning.
• Self-Hosted (Enterprise) — Docker + k8s deployment in your infra.
• Threads + Sessions — Group traces into conversational sessions.