Galileo API + MCP vs LangSmith API + MCP

Galileo API + MCP

OpenAPI 3.1 spec with 184 paths and 244 operations. No status page, no published rate limits and no SLA.

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).

Galileo API + MCP

1. Check which side the account lives on first. Pre-August Galileo accounts use api.galileo.ai, Splunk SaaS accounts use app.{realm}.observability.splunkcloud.com/ao/api/
2. Send the key as Splunk-AO-API-Key. The current spec no longer lists Galileo-API-Key
3. Page list endpoints with limit and starting_token
4. Use the error catalogue's retriable flag to decide whether to retry. 429s carry no documented Retry-After
5. Use the REST API to read traces. The MCP server mostly creates datasets and prompts

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