Use this skill when implementing logging, metrics, distributed tracing, alerting, or defining SLOs. Triggers on structured logging, Prometheus, Grafana, OpenTelemetry, Datadog, distributed tracing, error tracking, dashboards, alert fatigue, SLIs, SLOs, error budgets, and any task requiring system observability or monitoring setup.
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Use this skill when implementing logging, metrics, distributed tracing, alerting, or defining SLOs. Triggers on structured logging, Prometheus, Grafana, OpenTelemetry, Datadog, distributed tracing, error tracking, dashboards, alert fatigue, SLIs, SLOs, error budgets, and any task requiring system observability or monitoring setup.
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Observability
Observability is the ability to understand what a system is doing from the outside by
examining its outputs - without needing to modify the system or guess at internals.
The three pillars are logs (what happened), metrics (how the system is
performing), and traces (where time is spent across service boundaries). These
pillars are only useful when correlated - a spike in your p99 metric should link to
traces, and those traces should link to logs. Invest in correlation from day one, not
as a retrofit.
When to use this skill
Trigger this skill when the user:
Adds structured logging to a service (pino, winston, log4j, Python logging)
Instruments code with OpenTelemetry or a vendor SDK (Datadog, New Relic, Honeycomb)
Defines SLIs, SLOs, or error budgets for a service
Builds a Grafana or Datadog dashboard
Writes Prometheus alerting rules or configures PagerDuty/Opsgenie routing
Tracks an incident and needs to correlate logs/traces/metrics
Do NOT trigger this skill for:
Pure infrastructure provisioning (Terraform, Kubernetes YAML) - those are ops/IaC concerns
Application performance profiling of CPU/memory at the code level (use a performance-engineering skill)
Key principles
Structured logging always - Every log line should be machine-parseable JSON with
consistent fields. Plain-text logs cannot be queried, filtered, or aggregated at
scale. Correlation IDs are non-negotiable.
USE for resources, RED for services - Resources (CPU, memory, connections) are
measured with Utilization/Saturation/Errors. Services (APIs, queues) are measured with
Rate/Errors/Duration. Knowing which method applies tells you which metrics to instrument
before you write a single line of code.
Instrument at boundaries - Service ingress/egress, database calls, external HTTP
calls, and message queue produce/consume operations are the minimum instrumentation
surface. Everything else is optional until proven necessary.
Alert on symptoms, not causes - Alert when users are impacted (high error rate,
high latency). Do not page on CPU at 80% or a memory warning - those are causes to
investigate, not symptoms to wake someone up for.
SLOs drive decisions - Every reliability trade-off should reference an error budget.
If budget is healthy, ship features. If budget is burning, stop and fix reliability.
SLOs without error budgets are just numbers on a slide.
Aggregated numbers over time, dashboards, alerting
Traces
Where did time go?
Request flow across services, latency attribution
Cardinality
Every unique combination of label values in a metric creates a new time series in your
metrics backend. user_id as a metric label will create millions of time series and
kill Prometheus. Keep metric label cardinality under ~100 unique values per label.
Use logs or traces for high-cardinality data (user IDs, request IDs, emails).
Exemplars
Exemplars are trace IDs embedded in metric data points. When you see a p99 spike on
a histogram, an exemplar lets you jump directly to a trace that caused it. OpenTelemetry
and Prometheus support exemplars natively. Enable them - they are the bridge between
metrics and traces.
Context propagation
Context propagation is the mechanism by which a trace ID flows through service boundaries.
The W3C traceparent header is the standard format. Every service must: extract the
header on ingress, attach it to async context, and inject it into all outbound calls.
Failing to propagate breaks trace continuity silently.
SLI / SLO / Error budget
SLI (Service Level Indicator): A measurement of service behavior users care about.
Example: successful_requests / total_requests
SLO (Service Level Objective): A target for an SLI over a time window.
Example: 99.9% of requests succeed within 300ms, measured over 30 days
Error budget:1 - SLO. For a 99.9% SLO, the budget is 0.1% - about 43 minutes
of downtime per month. Burn rate measures how fast you consume it.
Common tasks
Set up structured logging
Use pino for Node.js (fastest), winston for flexibility. Always include a correlation
ID middleware that attaches traceId to every log automatically.
Load instrumentation.ts before your app with node --require ./dist/instrumentation.js server.js.
See references/opentelemetry-setup.md for exporters, processors, and Python setup.
Define SLIs and SLOs
Define SLIs from the user's perspective first, then map to metrics you can measure.
# slos.yaml - document alongside your serviceservice:order-apislos:# Availability: are requests succeeding?-name:availabilitydescription:Fractionofrequeststhatreturnnon-5xxresponsessli:successful_requests/total_requests# status < 500target:99.9%window:30derror_budget_minutes:43.8# Latency: are requests fast enough?-name:latency-p99description:99thpercentileofrequestdurationunder500mssli:requests_under_500ms/total_requeststarget:99.0%window:30d# Correctness: are responses valid? (measured via synthetic probes or sampling)-name:correctnessdescription:Fractionoforderconfirmationsthatpassintegritychecksli:valid_order_confirmations/total_order_confirmationstarget:99.95%window:30d
SLO burn rate formulas:
error_budget = 1 - slo_target # 0.001 for 99.9%
burn_rate = observed_error_rate / error_budget
time_to_exhaustion = window_hours / burn_rate
# Fast burn (page now): 14.4x - exhausts 30d budget in 2 days
# Slow burn (ticket): 3x - exhausts 30d budget in 10 days
Create effective dashboards
Use the RED method layout. Eight to twelve panels per dashboard. Link to detail dashboards
for drill-down rather than putting everything on one page.
Add deploy annotations (vertical lines) so you can correlate deployments with incidents
Set panel thresholds to match your SLO targets (green/yellow/red)
Set up alerting without alert fatigue
Define severity tiers before writing a single rule. Map each tier to a routing target.
# Example Prometheus alerting rules (alerts.yaml)groups:-name:order-api.slorules:# P1: fast burn - exhausts 30d budget in 2 days-alert:HighErrorBudgetBurnexpr:|
(
rate(http_requests_errors_total[1h]) /
rate(http_requests_total[1h])
) > (14.4 * 0.001)
for:2mlabels:severity:p1team:platformannotations:summary:"Error budget burning at 14x+ rate"runbook:"https://runbooks.internal/order-api/high-error-burn"dashboard:"https://grafana.internal/d/order-api"# P3: slow burn - ticket, investigate during business hours-alert:SlowErrorBudgetBurnexpr:|
(
rate(http_requests_errors_total[6h]) /
rate(http_requests_total[6h])
) > (3 * 0.001)
for:1hlabels:severity:p3team:platformannotations:summary:"Error budget burning at 3x rate - investigate during business hours"
Routing rules (Opsgenie / PagerDuty):
severity=p1 -> Page primary on-call immediately
severity=p2 -> Page primary on-call during business hours, silent at night
severity=p3 -> Create Jira ticket, no page
severity=p4 -> Slack notification only
Every alert must have: a runbook link, an owner team, and a dashboard link.
If an alert fires and nobody knows what to do, the runbook is missing.
Implement distributed tracing
Instrument at service boundaries. Propagate context via W3C traceparent. Add attributes
that make traces searchable (user ID, order ID, tenant ID - as trace attributes, not
metric labels).
Keep cardinality < 100 per label; use traces for high-cardinality data
Alerting on causes (CPU > 80%)
Wakes humans for non-user-impacting events
Alert on symptoms (error rate, latency SLO burn)
No sampling strategy for traces
100% trace collection at scale is cost-prohibitive
Start at 10% head-based, add tail-based for errors
SLOs without error budgets
SLO becomes a vanity target with no operational consequence
Define budget, burn rate thresholds, and what changes at each level
Missing runbooks on alerts
On-call doesn't know what to do, wasted time in incidents
Every alert ships with a runbook before it goes to production
Gotchas
Cardinality explosion kills Prometheus - Adding a label with high cardinality (user_id, request_id, IP address) creates a new time series per unique value. A single bad label can OOM a Prometheus instance overnight. Always check cardinality before adding labels; use traces or logs for high-cardinality data.
Context propagation breaks at async boundaries - In Node.js, if you use setTimeout, setImmediate, or create a new Promise chain without explicitly passing context.active(), the trace context is lost and spans appear as orphan roots. Use AsyncLocalStorage-aware frameworks or manually propagate context with context.with(ctx, fn).
100% trace sampling in production is unsustainable - At any real scale, sampling every trace destroys budget and storage. Start at 10% head-based sampling with tail-based sampling for errors. The default AlwaysOnSampler in OTel SDKs is NOT suitable for production.
SLO burn rate alerts on short windows produce noise - A single spike in errors can trigger a "fast burn" alert that resolves in minutes. Pair fast-window alerts (1h) with slow-window alerts (6h) using multi-window alerting. Alert only when both windows exceed the threshold simultaneously.
Structured logging without redaction leaks secrets - pino and winston log entire objects by default. Passing req or body without a redact config will log Authorization headers, passwords, and tokens in plain text. Always configure the redact option before shipping to production.
References
references/opentelemetry-setup.md - OTel SDK setup for Node.js and Python, exporters,
processors, and sampling configuration
Load the references file when the task involves wiring up OpenTelemetry from scratch,
configuring exporters, or setting up the collector pipeline. The skill above is enough
for instrumentation patterns and SLO definitions.
Companion check
On first activation of this skill in a conversation: check which companion skills are installed by running ls ~/.claude/skills/ ~/.agent/skills/ ~/.agents/skills/ .claude/skills/ .agent/skills/ .agents/skills/ 2>/dev/null. Compare the results against the recommended_skills field in this file's frontmatter. For any that are missing, mention them once and offer to install:
