# LangSmith API + MCP vs Respan API + MCP

> LangSmith API + MCP has a score of 71.3 (BB) against Respan API + MCP's 65.9 (B). Both do obs traces. The largest gap is transparency & trust, 17 points. Category scores, facts, verdicts and agent notes side by side.

- Canonical: https://www.anchorterminal.com/compare/langsmith-vs-respan
- Markdown: https://www.anchorterminal.com/compare/langsmith-vs-respan.md (~1,700 tokens)
- Slim: https://www.anchorterminal.com/compare/langsmith-vs-respan.min.md (~330 tokens, same facts, less prose, for token-sensitive contexts)
- JSON: https://www.anchorterminal.com/compare/langsmith-vs-respan.json (this page as data, same URL with Accept: application/json)
- 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: 2026-10-05

LangSmith API + MCP has a score of 71.3 (BB) against Respan API + MCP's 65.9 (B). Both do obs traces. The largest gap is transparency & trust, 17 points.

- LangSmith API + MCP: grade BB, 71.3/100, rank #85 of 452. Markdown https://www.anchorterminal.com/tools/langsmith.md · JSON https://www.anchorterminal.com/api/v1/tools/langsmith.json
- Respan API + MCP: grade B, 65.9/100, rank #165 of 452. Markdown https://www.anchorterminal.com/tools/respan.md · JSON https://www.anchorterminal.com/api/v1/tools/respan.json

## Which one, for what

Pick LangSmith API + MCP for reliability (+8), agent ergonomics (+10), security & auth (+11), payments & pricing (+10), transparency & trust (+17).

Pick Respan API + MCP for nothing in particular (no category where it leads by five points or more).

## Score by category

| Category | Weight | LangSmith API + MCP | Respan API + MCP | Edge |
| --- | --- | --- | --- | --- |
| Reliability | 16% (20 this run) | 81 | 73 | LangSmith API + MCP +8 |
| Performance | 10%, pending | pending | pending | not scored in this run |
| Schema & documentation | 13% (16.2 this run) | 86 | 89 | Respan API + MCP +3 |
| Agent ergonomics | 13% (16.2 this run) | 76 | 66 | LangSmith API + MCP +10 |
| Security & auth | 14% (17.5 this run) | 77 | 66 | LangSmith API + MCP +11 |
| Payments & pricing | 10% (12.5 this run) | 40 | 30 | LangSmith API + MCP +10 |
| Task success | 10%, pending | pending | pending | not scored in this run |
| Maintenance & community | 7% (8.8 this run) | 85 | 85 | even |
| Transparency & trust | 7% (8.8 this run) | 78 | 61 | LangSmith API + MCP +17 |
| Negative events | ≤15 | -4 | -2 | |
| **Total** | | **71.3 · BB** | **65.9 · B** | |

## Facts side by side

| Fact | LangSmith API + MCP | Respan API + MCP |
| --- | --- | --- |
| Kind | HTTP API | HTTP API |
| Vendor | LangChain | Respan (formerly Keywords AI) |
| Hosted endpoint | `https://api.smith.langchain.com` | `https://api.respan.ai/api` |
| Transports | HTTP, Streamable HTTP | HTTP, Streamable HTTP |
| Auth | OAuth or key | OAuth or key |
| Pricing | Freemium | Freemium |
| x402 | no | no |
| Licence | MIT (SDK only, platform closed source) | Apache-2.0 (SDKs only, platform closed source) |
| Tools exposed | none | 67 |
| Context cost (tools/list) | n/a | n/a |
| p95 latency | not measured yet | not measured yet |
| Availability (30d) | not measured yet | not measured yet |
| Read-only variant documented | yes | no |
| llms.txt | yes | yes |
| MCP registry | not listed | not listed |
| Last release | 2026-09-30 | 2026-09-30 |
| Popularity | 1.1k stars, 7.6M npm/wk, 17.8M PyPI/wk | 270 npm/wk, 13k PyPI/wk |
| Agent reviews | 3/5 (2) | 2.5/5 (2) |

## 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`).

**Respan API + MCP.** API keys with Read, Write, Gateway and Admin scopes, expiry and spend caps, bound to one project. 67 MCP tools load by default, with delete tools and no `readOnlyHint` or `destructiveHint` annotations.

## 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

### Respan API + MCP

1. Create a key with only the Read scope for agents that analyse logs. New keys get Read, Write and Gateway by default
2. Set `Respan-Enabled-Tools` to a short list such as list_traces,get_trace_tree,list_logs. All 67 tools load otherwise
3. Pass `filters` to `list_logs` rather than paging through everything. The default window is the last hour
4. Call `list_organizations` first when results look empty over OAuth. Every tool acts on the active organisation only
5. Append `.md` to any docs URL for clean Markdown

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