Loki Tail

An MCP server for Grafana Loki, designed around how LLMs actually query logs: compact output, hard row caps, and a fuzzy container-name rescue that turns the classic empty-result-because-wrong-name failure into an auto-corrected retry or an actionable suggestion list. Built on the Python MCP SDK (FastMCP); runs as a local stdio server or a containerized Streamable HTTP service with bearer auth.

Tools

Tool	Notes
loki_tail_container	"What is service X saying?" — the primary tool. Accepts approximate names: service vocabulary (vpn, proxy), bare names (sonarr), typos. On zero results it distinguishes valid-but-quiet from unknown name, auto-substitutes a unique fuzzy match (flagged in the output), or suggests candidates.
loki_query_range	Raw LogQL range query — multi-container correlation ({container=~"a|b"} |= "...") and metric queries (count_over_time(...)).
loki_query_instant	Instant query at a point in time (metric queries).
loki_list_containers	Durable container names (ephemeral CI/batch names hidden).
loki_list_labels / loki_list_label_values	Raw label discovery.
loki_patterns	Log pattern mining — thousands of lines → ranked recurring templates with counts. Requires the server-side pattern ingester (pattern_ingester.enabled: true).
loki_log_volume	Rank containers by log bytes over a window — "which service suddenly got noisy".
loki_detected_fields	Fields Loki can auto-extract from a stream (name/type/cardinality/parser) — discover | logfmt | status>=500 opportunities before writing LogQL.

The name-resolution design

Matching always runs against live label values, never a hardcoded list, so it survives renames. Resolution tries, in order: exact match → alias vocabulary → substring both ways → typo distance (difflib). A unique candidate is tailed automatically and flagged; multiple candidates become a ranked suggestion list. Auto-generated container names (docker/podman adjective_noun, hex-suffixed batch workers) are filtered out of discovery and suggestions but stay queryable via raw LogQL.

The built-in alias vocabulary covers the common self-hosted stack (vpn→gluetun, proxy→traefik, movies→radarr, …). Entries whose targets don't exist in your fleet are inert; extend with your own via LOKI_ALIASES.

Quick start (stdio)

// e.g. Claude Desktop claude_desktop_config.json / Claude Code .mcp.json
{
  "mcpServers": {
    "loki": {
      "command": "uv",
      "args": ["run", "--project", "/path/to/loki-tail-mcp", "loki-tail-mcp", "--stdio"],
      "env": { "LOKI_URL": "http://your-loki-host:3100" }
    }
  }
}

stdio mode has no network surface and skips bearer auth — the client owns the process.

HTTP mode (container)

The bundled Containerfile builds a Streamable HTTP server at /mcp (stateless — restarts never strand client sessions). HTTP mode refuses to start without MCP_BEARER_TOKEN; clients authenticate with Authorization: Bearer <token>.

podman build -t loki-tail-mcp .   # or: docker build -t loki-tail-mcp .
podman run -d --name loki-tail-mcp -p 8325:8325 \
  -e LOKI_URL=http://your-loki-host:3100 \
  -e MCP_BEARER_TOKEN=some-long-random-token \
  loki-tail-mcp

loki_tail_mcp.healthcheck does a full HTTP round-trip to /mcp (the 401 counts as alive); wire it to your container healthcheck. Terminate TLS at a reverse proxy — the server itself speaks plain HTTP.

Configuration

Env var	Default	Purpose
LOKI_URL	http://loki:3100	Loki base URL.
LOKI_TENANT_ID	(empty)	Sent as X-Scope-OrgID for multi-tenant Loki.
LOKI_BASIC_AUTH	(empty)	user:password for a basic-auth-fronted Loki (reverse proxy, Grafana Cloud).
LOKI_TIMEOUT	30	Upstream request timeout (s).
LOKI_DEFAULT_LIMIT / LOKI_MAX_LIMIT	100 / 1000	Row caps — Loki will happily return millions of rows; an MCP client will happily feed them to an LLM. Neither is what you want.
LOKI_ALIASES	(empty)	Extra vocabulary merged over the built-ins: term=fragment or term=frag|frag2, comma-separated (e.g. cache=redis|valkey,db=postgres).
LOKI_EPHEMERAL_PATTERNS	(built-ins)	Comma-separated regexes marking names as ephemeral; replaces the defaults when set.
PORT	8325	HTTP listen port.
MCP_BEARER_TOKEN	(empty)	Required in HTTP mode; server refuses to start without it. Not used in --stdio mode.

Testing

# Full suite — mocked HTTP + pure resolution logic, no Loki needed
uv run --extra test pytest tests/ -v

License

MIT