RelayPlane vs PromptLayer
PromptLayer is a prompt logging, versioning, and analytics platform that wraps OpenAI and Anthropic SDK calls. RelayPlane is an MIT-licensed npm proxy that intercepts LLM requests for real-time cost control and model routing. Here is how they compare for teams building and governing AI applications.
TL;DR
Choose RelayPlane when you want:
- npm install and running in 30 seconds with no account or SDK setup
- Real-time cost control and model routing in the request path
- Local SQLite cost tracking with no data leaving your machine
- OpenAI-compatible drop-in with one baseURL swap, zero code changes
- Works with Claude Code, Cursor, and any tool you cannot instrument
PromptLayer may work for you if you need:
- A hosted dashboard for searching and filtering all logged LLM requests
- A prompt registry for versioning and publishing prompt templates
- Cost analytics broken down per prompt template and model
- A/B testing prompt variants with outcome tracking
Feature Comparison
| Feature | RelayPlane | PromptLayer |
|---|---|---|
| Product type RelayPlane sits in the critical path of every LLM request: it intercepts, routes, and logs each call transparently at the network level. PromptLayer is an application-layer platform that wraps OpenAI and Anthropic SDK calls to log request and response data. PromptLayer does not proxy or route requests -- it observes calls you explicitly instrument. | npm-native LLM proxy and gateway (local-first) | Prompt logging, versioning, and analytics platform (application-layer SDK wrapper) |
| Install method RelayPlane ships as a standalone npm binary: one command and you are proxying requests. PromptLayer requires installing its SDK and replacing direct OpenAI or Anthropic calls with PromptLayer wrapper calls. Every prompt that should appear in the PromptLayer dashboard must be explicitly routed through the PromptLayer client. | npm install -g @relayplane/proxy | pip install promptlayer (Python) or npm install promptlayer (JS), SDK wrapping required |
| No account required RelayPlane starts with zero signup, zero credit card, and zero cloud dependency. PromptLayer requires creating an account and obtaining an API key before any request logging or analytics data is collected. There is no local or offline mode. | ||
| Free tier RelayPlane has no request cap or free tier limit. PromptLayer's free tier is limited to 2,000 requests per month. The Starter plan at $30/month covers 20,000 requests, and the Pro plan at $100/month covers 100,000 requests. Enterprise pricing is custom. | MIT open source, no usage limits, fully free to self-host | Free tier: 2,000 requests/month. Starter $30/month (20k req). Pro $100/month (100k req). Enterprise: custom. |
| No code changes required RelayPlane requires zero application code changes. Set OPENAI_BASE_URL=http://localhost:4100 and your existing code is automatically proxied. PromptLayer requires replacing every OpenAI or Anthropic call with a PromptLayer wrapper call that routes through the PromptLayer SDK. Existing code must be rewritten to adopt the platform. | ||
| Request interception (proxy mode) RelayPlane intercepts every LLM request transparently via a baseURL swap. No code changes needed beyond pointing your client at localhost:4100. PromptLayer requires explicit SDK integration in your application code and does not operate as an HTTP proxy that captures all outbound requests. | ||
| Model routing and fallback RelayPlane routes requests to different models based on complexity and cost, with automatic fallback on provider failures. PromptLayer logs which model each request used and can store prompt templates targeting specific models, but does not dynamically route requests or switch providers when one fails. | ||
| Local SQLite cost tracking RelayPlane logs every request's exact dollar cost in local SQLite with no data leaving your machine. PromptLayer tracks token usage and cost per request in its cloud dashboard, but this data is stored on PromptLayer's servers and requires an active account to access. | ||
| No data leaves your machine RelayPlane runs entirely on localhost by default with zero external telemetry. PromptLayer sends all prompt inputs, outputs, metadata, and analytics to PromptLayer's cloud servers. Every logged request and response is stored in PromptLayer's infrastructure. | ||
| Spend governance and budget limits RelayPlane can enforce spend limits and route away from expensive models when budgets are exceeded. PromptLayer tracks per-request cost in its analytics dashboard but has no mechanism to block, reroute, or cap spending on live requests. | ||
| OpenAI-compatible drop-in RelayPlane exposes an OpenAI-compatible endpoint: set OPENAI_BASE_URL=http://localhost:4100 and your existing code works unchanged. PromptLayer requires calling its own wrapper methods instead of the standard OpenAI or Anthropic client, so existing code must be adapted to the PromptLayer API surface. | ||
| Works with Claude Code and Cursor RelayPlane is designed for Claude Code, Cursor, Windsurf, and Aider with direct integration docs. PromptLayer is an application-layer SDK that cannot intercept traffic from AI coding assistants you do not control the source code of. | Not applicable (SDK integration, not a proxy) | |
| Real-time request governance RelayPlane acts on every request as it happens: routing, capping, and controlling LLM calls before they reach the provider. PromptLayer logs requests after they complete. It observes what happened but cannot intervene in the request path. | ||
| Prompt logging and request history Both tools log prompt inputs and outputs. RelayPlane stores logs locally in SQLite with no cloud dependency. PromptLayer's core capability is a searchable cloud dashboard of every logged request, with filtering by model, cost, tags, and date range. | Local SQLite log | |
| Prompt versioning and templates PromptLayer's central feature is a prompt registry where you can store, version, and publish prompt templates. Teams can pull the latest version of a prompt at runtime using the PromptLayer SDK, so prompt changes do not require code deployments. RelayPlane focuses on cost control and routing rather than prompt lifecycle management. | ||
| Cost analytics dashboard PromptLayer provides a cloud analytics dashboard with cost breakdowns per model, per prompt template, and per tag. RelayPlane tracks cost locally in SQLite. For teams that need a hosted, searchable analytics UI, PromptLayer's dashboard is more feature-rich than RelayPlane's local logs. | Local only | |
| A/B testing prompts PromptLayer supports running experiments that compare prompt variants by logging outcomes for each variant. RelayPlane routes based on cost and model capability, not prompt variant experiments. | ||
| Open source RelayPlane is MIT licensed end to end. PromptLayer is a closed-source SaaS product. There is no self-hosted or open-source edition of the PromptLayer platform. | MIT licensed |
Why Teams Choose RelayPlane When They Need Cost Control, Not Just Prompt Logging
A proxy intercepts every request. An SDK wrapper only captures what you explicitly instrument.
PromptLayer is an application-layer platform: you replace your OpenAI or Anthropic calls with PromptLayer wrapper calls, and only those wrapped calls appear in the dashboard. If you have existing code, a third-party library, or a tool like Claude Code making LLM requests, PromptLayer cannot see or control them. RelayPlane is an HTTP proxy that intercepts all outbound LLM traffic at the network level. Set one environment variable and every LLM call from any application, library, or tool is captured, tracked, and governed without changing a single line of code.
npm install in 30 seconds vs SDK wrapping plus account setup.
npm install -g @relayplane/proxy and you are proxying requests. PromptLayer requires creating an account, obtaining an API key, installing the SDK (pip install promptlayer or npm install promptlayer), and rewriting each LLM call to use the PromptLayer client. For new projects this is manageable. For existing codebases with many LLM calls already using the standard OpenAI or Anthropic SDK, the migration effort is substantial. RelayPlane's HTTP proxy approach requires no migration: your existing client code continues to work unchanged.
Real-time cost control in the request path, not just analytics after the fact.
PromptLayer tracks the cost of each logged call in its cloud analytics dashboard, which is useful for understanding spending patterns after requests complete. But it cannot stop you from spending. RelayPlane tracks cost and can enforce it: budget limits, routing to cheaper models when thresholds are hit, automatic fallback when providers return errors. For agentic workloads that can run for minutes and burn unexpected tokens, having a proxy that caps spending in real time is meaningfully different from a dashboard that shows you what happened after the money was spent.
Use both tools together: RelayPlane for routing, PromptLayer for prompt management.
RelayPlane and PromptLayer address different problems and can complement each other. If your team uses PromptLayer to manage prompt versions, run A/B experiments, and analyze cost per prompt template, you can still run RelayPlane as the proxy layer underneath. RelayPlane handles routing and cost control at the infrastructure level. PromptLayer handles prompt iteration and analytics at the application level. You do not have to choose one or the other if your workflow needs both.
PromptLayer Solves Prompt Observability Problems. RelayPlane Solves Cost Control Problems.
PromptLayer is a focused product for teams who need to log every LLM call, track prompt versions, and analyze cost and usage across a central dashboard. Founded in 2022, it supports Python and JavaScript SDKs and works as a thin wrapper around OpenAI and Anthropic clients. Its prompt registry lets teams store and version prompt templates separately from code, so prompt changes can be deployed without code releases. For teams that need a searchable audit trail of every LLM call and a structured way to iterate on prompts, PromptLayer provides a focused, purpose-built toolset.
But PromptLayer cannot route requests, enforce budget limits, or intercept traffic from tools you do not control. It requires rewriting your LLM calls to use the PromptLayer SDK. It does not work with Claude Code, Cursor, or other AI coding assistants because those tools do not expose SDK integration points. The free tier is capped at 2,000 requests per month, and paid plans start at $30/month. If you want to start tracking and controlling LLM costs today across any framework, any language, and any tool you use, RelayPlane installs in one npm command and runs on localhost with zero account or code changes required.
PromptLayer Pricing at a Glance
| Plan | Price | Account Required | Key Limits |
|---|---|---|---|
| Free | $0/month | Yes | 2,000 requests/month |
| Starter | $30/month | Yes | 20,000 requests/month |
| Pro | $100/month | Yes | 100,000 requests/month |
| Enterprise | Custom pricing | Yes | Custom limits, dedicated support |
| RelayPlane | Free (MIT) | No | No caps, no limits, runs on localhost |
Get Running in 30 Seconds
No account. No SDK wrapping. No rewriting your LLM calls: