Spanlens runs on your own machine — the client starts it, so there is no endpoint to ping. 66 installs a week from npm. Last commit 6 Nov 2026.
Query Spanlens LLM observability from Cursor, Claude Desktop, or Continue via MCP.
What the code does
We read the source, 3 d ago · rules 995398eba69f
What this server is able to do. For an MCP server this is often the job itself — a terminal server runs commands because that is what it is for. Listed so you know what you are plugging in, not as an accusation.
const value = await redis.eval(
const child = spawn(pm, args, {
path = os.path.join(cwd, filename)
proc = subprocess.run( # noqa: S603 - argv is a fixed list, no shell
aria-label={`Delete ${a.name}`}
Is this your server and something here is wrong? Tell us — corrections are free and do not require a plan.
This code can reach further than it looks
We found places where it runs commands, builds paths or queries from values it is given. None of that is a flaw by itself — it becomes one when the code changes, and code changes quietly between releases. We re-read it on every one.
Connect this server
This server runs on your own machine — install it with the package manager and the client starts it for you. Package name taken from the official registry entry.
claude mcp add mcp-server -e 'SPANLENS_API_KEY=<SPANLENS_API_KEY>' -- npx -y @spanlens/mcp-server{
"mcpServers": {
"mcp-server": {
"command": "npx",
"args": [
"-y",
"@spanlens/mcp-server"
],
"env": {
"SPANLENS_API_KEY": "<SPANLENS_API_KEY>"
}
}
}
}[mcp_servers.mcp-server]
command = "npx"
args = ["-y", "@spanlens/mcp-server"]
env = { SPANLENS_API_KEY = "<SPANLENS_API_KEY>" }{
"mcpServers": {
"mcp-server": {
"command": "npx",
"args": [
"-y",
"@spanlens/mcp-server"
],
"env": {
"SPANLENS_API_KEY": "<SPANLENS_API_KEY>"
}
}
}
}{
"servers": {
"mcp-server": {
"type": "stdio",
"command": "npx",
"args": [
"-y",
"@spanlens/mcp-server"
],
"env": {
"SPANLENS_API_KEY": "<SPANLENS_API_KEY>"
}
}
}
}Put your own value in place of
<SPANLENS_API_KEY> (Spanlens API key. Must be a scope=public key (sl_live_pub_*) issued from the Public Keys card at https://spanlens.io/projects — the server refuses to start with a full-access sl_live_* key).
The author’s registry entry marks it as required.
Optional settings from the registry entry, left out of the block above:
SPANLENS_BASE_URL (Override the API endpoint for self-hosted Spanlens. Default: https://api.spanlens.io).
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Spanlens — questions
Answers built from our own checks of this server.