Probe0 vs LangSmith
LangSmith exists to explain what an agent did, at team scale, in a hosted dashboard you can share. Probe0 exists to reduce what a coding agent costs on one developer's machine, and it does that work before the request leaves the laptop.
LangChain's commercial, framework-agnostic platform for tracing, evaluating and monitoring LLM agents, delivered as hosted SaaS with a self-hosted option on its Enterprise tier.
| Feature | Probe0 | LangSmith | Edge |
|---|---|---|---|
| Where prompts and cost data live | On your Mac. There is no Probe0 server to send anything to. | Hosted SaaS by default; self-hosted and hybrid on Enterprise. | Probe0 |
| Setup for one developer's coding agents | One local proxy plus a certificate, once. Claude Code, Codex and Cursor all route through it. | SDK, framework callback or a base_url swap, configured per application. | Probe0 |
| Response caching | Exact cache on local disk. A hit never touches the network at all. | No native response cache; caching is left to a separate proxy layer. | Probe0 |
| Semantic reuse without corrupting a run | Local vector index, strict similarity floor, refuses to match anything carrying tool calls. | No semantic matching layer to govern. | Probe0 |
| Working with a local model | Routes to a model already loaded in Ollama or LM Studio, retries weak answers on the cloud. | Can trace calls to a local model, but is not an inference or local routing layer. | Probe0 |
| Cheaper model first | Model Tiering tries the cheap model, escalates when needed. | LLM Gateway (public beta) does fallback routing on failure, not cost tiering. | Probe0 |
| Which process spent the money | Ledger records model, tokens, real cost, latency and the calling process. | Unified cost view across LLM calls plus custom costs for tools and retrieval. | Probe0 |
| Spend limits | Hard cap per run and per day. Warns, then pauses. | LangSmith LLM Gateway (public beta) enforces spend caps at org, workspace, user and key level. | Even |
| Trace search and evaluation | A local request ledger you can read and filter. No scoring. | Span-level trace store with sharing and alerts, plus LLM-as-judge, code evaluators and golden datasets. | Competitor |
LangSmith owns the part of this comparison I do not compete on: a persistent span-level trace store with an evaluation stack behind it, including LLM-as-judge and code-based evaluators, judges calibrated to human preference, side-by-side comparison across agent versions and one-click promotion of a production trace into a golden dataset. Everything else on this page is a dimension where I think Probe0 is the better answer for a developer running coding agents on their own Mac. Coding agents are chatty and repetitive, and most of the money goes to calls that were never worth a frontier model, which is a wire-level problem rather than an application-layer one. Probe0 sits on the machine as a proxy every agent CLI already trusts, so one certificate covers Claude Code, Codex and Cursor with nothing to configure per tool. LangSmith asks each application to opt in through an SDK, a framework callback or a base_url swap.
Each Probe0 module intercepts a different kind of waste. Local Routing hands a request to a model already resident in Ollama or LM Studio and quietly retries on the cloud when the answer comes back weak. Model Tiering tries the cheap model first. The Exact Cache lives on local disk and never touches the network. The Semantic Cache uses a local vector index with a strict similarity floor and refuses outright to match anything carrying tool calls, because a wrong hit there corrupts a run rather than just annoying you. Request Coalescing collapses simultaneous identical calls into one upstream request. Spend Guard enforces a hard cap per run and per day, warning first and then pausing, which is the behaviour I wanted when I was the one leaving an agent running unattended. Every module is individually switchable and reports what it saved, so you can turn one off and watch the number move.
The other difference is where the data sits. LangSmith is a remote collector by default, and self-hosting is an Enterprise-tier arrangement rather than something you switch on yourself. Probe0 has no server component at all, so prompts, responses and the cost ledger stay on your disk with nothing to opt out of. That ledger records which process made each call, which is the piece I found hardest to get any other way: it tells you that Cursor autocomplete, not your Claude Code session, ate two thirds of yesterday's spend. Because Probe0 knows real usage rather than estimates, it can also tell you when your subscription tier is above what you actually consume. LangSmith recently shipped its own LLM Gateway in public beta with spend caps, rate limits, PII redaction and fallback routing on the Plus and Enterprise plans, so the budget gap has narrowed. The gap that remains is caching, local inference and the fact that Probe0 costs nothing to run because it runs on hardware you already own.
The verdict
Pick LangSmith when your problem is agent quality and you need trace search, systematic evaluation and online monitoring across a product a team is shipping. For everything else on this page, and specifically if you are one developer whose bill comes from AI coding agents on a Mac, Probe0 is the choice: caching that answers without a network call, routing to a model already loaded locally, a cap that pauses instead of emailing you, per-process cost attribution, and no prompt leaving the machine. Start with Probe0, add LangSmith later if you end up needing evals.
Questions
- Is Probe0 a LangSmith alternative?
- Only for the cost and routing half of the job. Probe0 is a local LLM proxy that caches, routes to local LLMs and enforces spend caps for AI coding agents, and it records a full request ledger. It has no evaluation framework, no hosted trace UI and no team features, so it does not replace LangSmith for agent quality work.
- Does LangSmith cache LLM responses or reduce my token spend?
- LangSmith itself has no native response caching layer; that has historically been the job of a separate proxy. Its LLM Gateway product, in public beta on Plus and Enterprise plans, adds spend caps, rate limits and fallback routing, which controls what you are allowed to spend rather than removing duplicate calls before they happen.
- Can I use Probe0 and LangSmith together?
- Yes. Probe0 sits on your machine between your coding agent and the provider, so a served cache hit or a local model answer never reaches the provider at all, while anything your application traces to LangSmith continues to be traced. The two operate at different layers.
- Does Probe0 send my prompts anywhere?
- No. Probe0 runs entirely on your machine, the exact cache is local disk, the semantic index is a local vector store, and the cost ledger is a local file. There is no Probe0 server to send anything to. Sign-in exists via Google or GitHub for the account layer, and the request data stays local.