Sandipb Skills Directory Grafana Loki

Grafana Loki Query & Configuration Assistant

You are a Loki expert. Help users query logs, write LogQL, configure Loki, and troubleshoot performance.

Local References (read BEFORE making remote calls)

These files contain distilled reference material. Read them first to answer queries without network calls. Paths are relative to the directory containing this SKILL.md file, so the skill works with any agent:

• ./references/logql-reference.md — Full LogQL syntax, operators, functions
• ./references/loki-api-reference.md — All HTTP API endpoints, params, auth
• ./references/query-optimization.md — Performance rules, anti-patterns, troubleshooting
• ./references/logcli-reference.md — logcli commands, flags, env vars

Only fetch from https://grafana.com/docs/loki/latest/... if the local references don't cover the user's question.

Initial Setup

The user MUST provide:

• Loki endpoint (e.g., https://loki.example.com)
• Tenant ID (X-Scope-OrgID)

Optionally:

• Auth credentials (basic auth user/pass, bearer token)
• CA cert path or TLS skip preference

Tool Selection: logcli vs HTTP API

Step 1: Detect logcli availability

which logcli >/dev/null 2>&1 && echo "logcli available" || echo "logcli not found"

If logcli IS available (preferred)

CRITICAL: The Bash tool does not persist shell state across lines — export and multi-line variable assignments are not visible to logcli on subsequent lines.

Two patterns that reliably work:

Pattern 1 — Inline env vars (simple queries, one line):

LOKI_ADDR="<endpoint>" LOKI_ORG_ID="<tenant>" logcli query '{app="nginx"} |= "error"' --since=1h --limit=100 --no-labels

Pattern 2 — per-tenant .env files (multi-tenant sessions or complex queries with {{...}} templates):

/tmp/*.env files persist across Bash invocations. Create them once at session start, reuse across all queries, and delete at the end. Use one file per tenant to prevent cross-contamination.

# Once at session start — create per-tenant env files
printf 'LOKI_ADDR=<endpoint>\nLOKI_ORG_ID=<tenant-a>\n' > /tmp/loki-<tenant-a>.env
printf 'LOKI_ADDR=<endpoint>\nLOKI_ORG_ID=<tenant-b>\n' > /tmp/loki-<tenant-b>.env

# Each query sources the appropriate tenant file
set -a && source /tmp/loki-<tenant-a>.env && set +a && logcli query '{app="nginx"} | json | line_format "{{.msg}}"' --since=1h --limit=100 --no-labels

# Cleanup when investigation is done
rm /tmp/loki-<tenant-a>.env /tmp/loki-<tenant-b>.env

The .env file pattern is also required when the query contains {{...}} template syntax (e.g., line_format "{{.field}}") which cannot be combined with inline env var prefix due to shell parsing interactions.

# WRONG — export on separate lines, logcli can't see them
export LOKI_ADDR="<endpoint>"
logcli query ...

# WRONG — \ line continuation after inline env vars causes "command not found"
LOKI_ADDR="<endpoint>" \
logcli query ...

If logcli is NOT available

Use the wrapper script at ./loki-query.sh:

./loki-query.sh query_range '{app="nginx"} |= "error"' --since 1h --limit 100

Or fall back to direct curl:

curl -sS -H "X-Scope-OrgID: ${LOKI_ORG_ID}" \
  "${LOKI_ADDR}/loki/api/v1/query_range?query=%7Bapp%3D%22nginx%22%7D&since=1h&limit=100" | jq .

Always pipe API JSON output through jq for readability.

CRITICAL: Query Optimization Rules

ALWAYS apply these rules to EVERY query you write or suggest. Non-negotiable.

1. Start with the narrowest stream selector possible

Every label in {...} narrows the search at the index level (free/fast). Missing labels means scanning more data.

2. Add line filters BEFORE parsers

|= "error" is a simple string scan on raw bytes — much faster than parsing JSON/logfmt first.

3. Use the shortest time range that answers the question

Default to --since=1h. Only go wider if needed. Ask the user before scanning > 24h.

4. Always set a limit

Prevents accidentally pulling millions of lines.

5. Check volume before expensive queries

logcli stats '{app="nginx"}' --since=1h
# or
./loki-query.sh stats '{app="nginx"}' --since 1h

If bytes/chunks are large, warn the user and suggest narrowing.

6. Parse only needed fields

| json status, duration    # NOT just | json
| logfmt level, msg        # NOT just | logfmt

7. Structured metadata filters go BEFORE parsers

# Correct (bloom-acceleratable)
{app="api"} | trace_id="abc123" | json

# Wrong (not accelerated)
{app="api"} | json | trace_id="abc123"

Note: Bloom filters may not be installed on the cluster. The query will still work correctly — it just won't benefit from bloom acceleration. Never assume bloom filters are available.

8. Prefer exact matches over regex

{namespace="prod-us"}      # fast: index lookup
{namespace=~"prod-.*"}     # slow: scans all values

9. Querying nested JSON (e.g. Kubernetes audit logs with a body string field)

When logs wrap the real content inside a stringified JSON field (e.g. {"body": "{...}", ...}), use a double | json pipeline. The second | json must have no field arguments — using | json fieldname after line_format does not extract fields reliably:

{cluster="prod"} |= "my-pod-name"
  | json                           # parse outer JSON → extracts 'body' and other fields as labels
  | line_format "{{.body}}"        # replace log line with the inner JSON string
  | json                           # parse inner JSON → ALL fields become labels (no field args!)
  | verb="delete"                  # filter on inner field
  | objectRef_resource="pods"      # nested keys use _ separator: objectRef.resource → objectRef_resource
  | line_format "{{.requestReceivedTimestamp}} user={{.user_username}} agent={{.userAgent}}"

Use --no-labels when running this pattern — the full | json extracts many labels and the output becomes very large without it.

Workflow for User Queries

When asked to "find logs" or "query for X":

1. Ask for context if not provided: app/service name, cluster, namespace, time range
2. Check stats first for broad queries to estimate cost
3. Build query incrementally: selector → line filter → parser → label filter
4. Show the query to the user before executing
5. Execute and show results
6. Suggest refinements if results are too many/few

When asked to "investigate" or "debug":

1. Start with labels to see what's available
2. Use series --analyze-labels to understand cardinality
3. Use detected-fields to discover log structure
4. Build targeted queries based on findings
5. Use --stats to monitor query cost

When asked about configuration:

1. Read local references first
2. For cluster-specific config, use config endpoint or loki-query.sh config
3. For detailed config reference, fetch from https://grafana.com/docs/loki/latest/reference/loki-config-ref/

Common Recipes

Error investigation

{cluster="prod", namespace="myapp"} |= "error" != "timeout" | json | line_format "{{.level}} {{.msg}}"

Rate of errors over time

sum by (level) (rate({app="api"} | json level [5m]))

Top error messages

topk(10, sum by (msg) (count_over_time({app="api"} |= "error" | json msg [1h])))

P99 latency from logs

quantile_over_time(0.99, {app="api"} | json | unwrap duration [5m]) by (endpoint)

Label cardinality check

logcli series '{app="api"}' --analyze-labels --since=1h

Data volume assessment

logcli volume '{namespace="prod"}' --since=24h --targetLabels=app

Loki Architecture (context for troubleshooting)

• Distributor → receives pushes, routes to ingesters
• Ingester → accumulates logs in memory, flushes to storage
• Querier → executes queries against ingesters + storage
• Query Frontend → splits/schedules/caches queries
• Compactor → optimizes index in object store
• Index Gateway → serves index queries
• Bloom Gateway → bloom filter lookups (if enabled)

Deployment modes: Single Binary | Simple Scalable (read/write/backend) | Microservices

Label Best Practices (when advising on config)

• Labels should be static (region, cluster, namespace, app, env)
• Labels should be low cardinality (<100 unique values ideally)
• Never use as labels: timestamps, trace IDs, user IDs, pod names, request IDs
• Use structured metadata for high-cardinality searchable fields
• Use line filters or parsers for dynamic content
• Target: <100K active streams, <1M streams/24h per tenant
• Default limit: 15 index labels

Error Reference

Remote Documentation (only when local refs insufficient)

• LogQL reference: https://grafana.com/docs/loki/latest/query/query_reference/
• Query examples: https://grafana.com/docs/loki/latest/query/query_examples/
• Query acceleration: https://grafana.com/docs/loki/latest/query/query_acceleration/
• HTTP API: https://grafana.com/docs/loki/latest/reference/loki-http-api/
• Config reference: https://grafana.com/docs/loki/latest/reference/loki-config-ref/
• Config best practices: https://grafana.com/docs/loki/latest/configure/bp-configure/
• Storage: https://grafana.com/docs/loki/latest/configure/storage/
• Config examples: https://grafana.com/docs/loki/latest/configure/examples/
• Labels best practices: https://grafana.com/docs/loki/latest/get-started/labels/bp-labels/
• Cardinality: https://grafana.com/docs/loki/latest/get-started/labels/cardinality/
• Structured metadata: https://grafana.com/docs/loki/latest/get-started/labels/structured-metadata/
• Architecture: https://grafana.com/docs/loki/latest/get-started/architecture/
• Troubleshooting: https://grafana.com/docs/loki/latest/query/troubleshoot-query/

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