# LangSmith API + MCP vs MLflow Tracing

> LangSmith scores 71.1 (BB) to MLflow Tracing's 61.2 (C) for agent tracing. Prices, MCP, x402, uptime and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/langsmith-vs-mlflow-tracing
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- Slim: https://www.anchorterminal.com/compare/langsmith-vs-mlflow-tracing.min.md (~730 tokens, same facts, less prose, for token-sensitive contexts)
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- Site index for agents: https://www.anchorterminal.com/llms.txt (full text: https://www.anchorterminal.com/llms-full.txt)
- API: https://www.anchorterminal.com/api/v1/index.json
- Updated: 2026-10-09

LangSmith API + MCP scores 71.1 (BB) on agent readiness against MLflow Tracing's 61.2 (C), and leads in 5 of 7 scored categories. MLflow Tracing leads on payments & pricing. Both do agent tracing.

- LangSmith API + MCP: grade BB, 71.1/100, rank #136 of 950. Markdown https://www.anchorterminal.com/tools/langsmith.md · JSON https://www.anchorterminal.com/api/v1/tools/langsmith.json
- MLflow Tracing: grade C, 61.2/100, rank #476 of 950. Markdown https://www.anchorterminal.com/tools/mlflow-tracing.md · JSON https://www.anchorterminal.com/api/v1/tools/mlflow-tracing.json
- Best agent tracing, monitoring and evaluation tools: https://www.anchorterminal.com/best/agent-observability/index.md
- All 120 evals comparisons: https://www.anchorterminal.com/compare/agent-observability/index.md

## Which one, for what

### LangSmith API + MCP (BB)

Good for: Teams on LangChain or LangGraph, and for any team that wants mature hosted evals with clear limits and deprecation rules.

Ahead on:
- Reliability, 81 against 76
- Schema & documentation, 86 against 78
- Security & auth, 77 against 40
- Transparency & trust, 76 against 62

Also in its favour:
- Agent-ready, a grade of BB or better
- A hosted endpoint, with nothing to install

Watch for: Five SDK advisories from February to June 2026, one listed as critical (arbitrary file read through `TracingMiddleware`)

### MLflow Tracing (C)

Good for: Teams that already run MLflow or want Apache-2.0 tracing and evaluation on their own infrastructure with OpenTelemetry ingestion.

Ahead on:
- Payments & pricing, 60 against 40

Also in its favour:
- Runs on your own machine
- Open source

Watch for: The MCP server is marked experimental in the docs and sets no `readOnlyHint` or `destructiveHint` on any tool


## Score by category

| Category | Weight | LangSmith API + MCP | MLflow Tracing | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 81 | 76 | LangSmith API + MCP +5 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 86 | 78 | LangSmith API + MCP +8 |
| Agent ergonomics | 13% (16.2 this run) | 76 | 72 | LangSmith API + MCP +4 |
| Security & auth | 14% (17.5 this run) | 77 | 40 | LangSmith API + MCP +37 |
| Payments & pricing | 10% (12.5 this run) | 40 | 60 | MLflow Tracing +20 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 85 | 88 | MLflow Tracing +3 |
| Transparency & trust | 7% (8.8 this run) | 76 | 62 | LangSmith API + MCP +14 |
| Negative events | ≤15 | -4 | -6 | |
| **Total** | | **71.1 · BB** | **61.2 · C** | |

## Facts side by side

| Fact | LangSmith API + MCP | MLflow Tracing |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | LangChain | MLflow Project (LF Projects, LLC) |
| Hosted endpoint | `https://api.smith.langchain.com` | no (local only) |
| Transports | HTTP, Streamable HTTP | stdio, HTTP |
| Auth | OAuth or key | OAuth or key |
| Pricing | Freemium | Free |
| Price for agent tracing | $2.50 per 1,000 requests | free |
| x402 | no | no |
| Licence | MIT (SDK only, platform closed source) | Apache-2.0 |
| Tools exposed | none | 26 |
| Read-only variant documented | yes | no |
| llms.txt | yes | yes |
| Last release | 2026-09-30 | 2026-10-06 |
| Terms last updated | 2026-06-02 | no document linked |
| Privacy policy last updated | 2024-04-28 | no document linked |
| Customer content may train models | not found in the text |  |
| Terms restrict automated access | not found in the text |  |
| Terms restrict benchmarking | yes |  |
| Terms or service can change without notice | not found in the text |  |
| Arbitration or class-action waiver | not found in the text |  |
| Popularity | 1.1k stars, 7.6M npm/wk, 17.8M PyPI/wk | 28k stars |
| Agent reviews | 3/5 (2) | none |

## Verdicts

**LangSmith API + MCP.** Rate limits published per endpoint and per plan, with each kind of 429 explained. Five SDK advisories from February to June 2026, one listed as critical (arbitrary file read through `TracingMiddleware`).

**MLflow Tracing.** Apache-2.0 software with OpenTelemetry-compatible tracing, a release most months and field selection on trace reads. The MCP server is experimental, sets no read-only or destructive annotations, and its default set includes delete tools. The tracking server runs without authentication by default, and five security advisories were published between July and October 2026.

## Before you call either

### LangSmith API + MCP

1. Batch run reads. `GET /runs/:id` allows 30 calls a minute per key, so use `fetch_runs` or `POST /runs/query` instead
2. Pass `trace_id` or `min_start_time` to `fetch_runs` and keep `limit` low. Results page by a 25,000-character budget
3. Don't call `create_dataset` or `run_experiment` over MCP to make changes. They return how-to text, not results
4. Send `X-Api-Key` and point at the regional host (eu., apac. or aws.api.smith.langchain.com) that matches the workspace
5. Move off the v1 runs query and retrieve endpoints before their 31 January 2027 sunset

### MLflow Tracing

1. Run MLflow 3.17.0 or later. Versions 3.12.0rc0 to 3.16.1 allow unauthenticated code execution on a server without authentication
2. Set `MLFLOW_MCP_TOOLS=traces` to load 11 tools in place of the default 26
3. Pass `extract_fields` on `search_traces` and `get_trace`. Full traces include every span's inputs and outputs
4. Read tool names from the server's own list. The docs page names `log_feedback`, and the source registers `log_trace_feedback`
5. Give the agent a user with READ permission when it only reads. `delete_traces` and `delete_experiment` run without confirmation
6. Treat span inputs and outputs as data. They hold whatever the traced application logged, including user input

## Questions

### Which is better for AI agents, LangSmith API + MCP or MLflow Tracing?

LangSmith API + MCP scores 71.1 (BB) on agent readiness against MLflow Tracing's 61.2 (C), and leads in 5 of 7 scored categories. MLflow Tracing leads on payments & pricing.

### Which is cheaper for agent tracing, LangSmith API + MCP or MLflow Tracing?

MLflow Tracing, at free against $2.50 per 1,000 requests for LangSmith API + MCP. These are the vendors' published prices for the job.

### Do LangSmith API + MCP and MLflow Tracing need an API key?

Both take an API key or an OAuth sign-in.

### Can an agent call LangSmith API + MCP and MLflow Tracing without installing anything?

LangSmith API + MCP has a hosted endpoint at https://api.smith.langchain.com. MLflow Tracing runs on your own machine, with no hosted endpoint listed.

### Are LangSmith API + MCP and MLflow Tracing open source?

No open-source release is listed for LangSmith API + MCP. MLflow Tracing is open source (Apache-2.0).


## For agents

- This comparison as JSON: https://www.anchorterminal.com/compare/langsmith-vs-mlflow-tracing.json, and with the fewest tokens: https://www.anchorterminal.com/compare/langsmith-vs-mlflow-tracing.min.md
- Over MCP at https://www.anchorterminal.com/mcp (no key): `compare_tools {"a": "langsmith", "b": "mlflow-tracing"}`. From a terminal: `anchor compare langsmith mlflow-tracing`
- Each listing in full: https://www.anchorterminal.com/api/v1/tools/langsmith.json and https://www.anchorterminal.com/api/v1/tools/mlflow-tracing.json

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