RelayPlane vs Braintrust: Cost Proxy vs Eval Platform
Braintrust is an eval and tracing platform built to help teams measure and improve LLM output quality. RelayPlane is a local-first cost proxy that cuts spend 40-60% by routing requests to the cheapest capable model. No account, no cloud, no eval overhead.
TL;DR
Choose RelayPlane when you want:
- 40-60% lower LLM spend via automatic complexity routing
- No account, no signup, no cloud in the request path
- Prompts and cost logs that stay on your machine only
- MIT open source, zero cloud dependency
Choose Braintrust when you need:
- Structured LLM evaluation with scoring and test datasets
- Prompt experiment tracking across model versions
- Team-wide tracing and output quality dashboards
Feature Comparison
| Feature | RelayPlane | Braintrust |
|---|---|---|
| Product focus RelayPlane is built to cut LLM costs by routing every request to the cheapest model capable of handling it. Braintrust is built for evaluating and tracing LLM output quality. Their proxy exists to capture calls for logging and scoring, not to optimize cost. | Cost intelligence + complexity routing | LLM eval + tracing platform |
| Install method RelayPlane is a single npm install with no account required. Braintrust requires creating an account, configuring a project, and issuing an API key before any request can be traced through their proxy. | npm install -g @relayplane/proxy | Account signup + API key |
| Primary use case RelayPlane routes simple queries to cheap models and complex queries to powerful ones, reducing spend automatically. Braintrust captures and scores LLM outputs so teams can run experiments and track quality over time. | Cut LLM costs 40-60% automatically | Eval, tracing, and prompt testing |
| Data privacy RelayPlane logs every request to local SQLite. No prompt or response leaves your machine. Braintrust is a cloud tracing platform, so your requests are routed through their infrastructure to enable logging, scoring, and the eval dashboard. | All data stays on device (SQLite) | Requests route through Braintrust cloud for tracing |
| No account required RelayPlane works entirely without an account. Braintrust requires registration and project setup before the proxy can be used. | ||
| Complexity routing RelayPlane automatically routes simple tasks to cheaper models like Haiku and complex tasks to Opus. Braintrust routes to the model you configure for your project. It does not perform complexity-based cost optimization. | ||
| Per-request cost tracking RelayPlane logs the exact token count and dollar cost of every request to local SQLite. Braintrust provides a cloud dashboard for usage and cost, but that data lives on their servers rather than yours. | SQLite per-request log (on-device) | Cloud dashboard (data on their servers) |
| Works with Claude Code / Cursor RelayPlane is designed as a drop-in proxy for Claude Code and Cursor via a baseURL swap and works seamlessly in that context. Braintrust can technically proxy IDE requests but is optimized for eval workflows, not local developer tooling. | Partial (eval-focused, not IDE proxy) | |
| Open source Both RelayPlane and the Braintrust proxy component are MIT licensed. RelayPlane is fully self-hosted with no cloud dependency. Braintrust's proxy is open source but designed to run through their cloud infrastructure for logging and eval. | MIT | MIT (proxy only) |
| Cost RelayPlane is free and self-hosted with no usage caps. Braintrust offers a free tier (1M spans) with paid plans from $249/mo for higher usage and team features. | Free | Free tier + paid plans |
| Per-tenant isolation RelayPlane isolates each tenant at the proxy layer so a runaway agent on one tenant cannot affect others. Braintrust is a single-tenant eval platform with no multi-tenant isolation concept. | First-class: separate request queues, budgets, and audit namespace per tenant | |
| Instant kill-switch API RelayPlane can instantly halt all traffic for a specific tenant via a single HTTP call using an in-memory flag. Braintrust has no equivalent mechanism. | POST /v1/tenants/:id/kill — halts all traffic within one request cycle | |
| Spec-match verification at proxy layer RelayPlane's spec-match verifies output inline, before the orchestrator marks a task done. Braintrust evals are typically run after-the-fact via their SDK, not as a gate in the proxy request path. | Built-in: LLM evaluates agent output against acceptance criteria before task completion | Evals run post-hoc via SDK; not integrated into the proxy request path |
| Compliance audit bundle export RelayPlane's audit log uses a checksum chain where modification of any entry is detectable. Braintrust provides trace exports but without cryptographic integrity guarantees. | Tamper-proof HMAC-chained audit log, exportable as JSON/CSV/JSONL | Span/trace export on paid plans; no cryptographic integrity chain |
Why Developers Choose RelayPlane Over Braintrust
Braintrust makes LLM calls visible. RelayPlane makes them cheaper.
Braintrust is an excellent tool for teams that need to evaluate output quality, run A/B prompt experiments, and trace which model produced which result. That is a legitimate and important use case. RelayPlane solves a different problem: it routes every request to the cheapest model that can handle the task, automatically, with no manual configuration required. For developers whose primary concern is spend rather than eval scores, RelayPlane is the right tool.
No cloud in the request path
When you use Braintrust as a proxy, your requests travel through their cloud infrastructure so they can be logged, traced, and scored. That is by design for an eval platform. RelayPlane runs entirely on your machine. Every request goes directly from your machine to the model provider, and every cost log is written to local SQLite. No prompt or response leaves your device. For developers working on sensitive codebases or who simply prefer not to route through a third-party cloud, RelayPlane provides the same proxy surface with zero data exposure.
30-second setup with no account
Braintrust requires creating an account, setting up a project, configuring an API key, and updating your request headers before you can start tracing. That setup is worth it if you need eval. If you just want cost tracking and model routing, RelayPlane is one npm install. Run npm install -g @relayplane/proxy, then relayplane init, then relayplane start, and your proxy is live on localhost:4100. No signup, no project configuration, no email confirmation.
MIT open source, zero cloud dependency
Both RelayPlane and the Braintrust proxy are MIT licensed. The difference is runtime architecture. Braintrust routes requests through their cloud to enable logging, tracing, and eval — that is the point of the product. RelayPlane runs entirely on your machine. No requests leave your device except to the model provider directly. No account to maintain, no cloud outage that affects your workflow, no vendor pricing change that breaks your setup.
Braintrust Solves Eval Quality. RelayPlane Solves Cost.
Braintrust is a well-built platform for teams that need structured LLM evaluation. If your job is to measure whether model outputs meet quality standards, run regression tests across prompt versions, and track scoring trends over time, Braintrust provides real tooling for that workflow. The proxy is a byproduct of their tracing architecture, not their core product.
RelayPlane is not an eval platform. It does not score outputs or run experiments. It does one thing: intercept every LLM request, classify the complexity, route to the cheapest capable model, and log the exact cost to local SQLite. For developers using Claude Code or Cursor who want to cut spend without changing how they work, RelayPlane is the tool. No eval, no tracing, no cloud. Just cheaper requests.
Get Running in 30 Seconds
No account. No eval setup. No cloud tracing. Just npm: