StaffSignal

Start Here

StaffSignal playbooks build the judgment that separates L5 answers from Staff answers. Each playbook is a complete preparation unit — not a problem catalog. Pick one and study it until you can defend the tradeoffs, failure modes, and ownership boundaries.

The Core 3

Free

If you only have time for three playbooks, start here. These cover the most common Staff interview surface area and build transferable judgment.

1
Rate Limiting
Appears in almost every system design. Forces you to reason about distributed state, consistency tradeoffs, and graceful degradation — the three pillars of Staff-level answers.
2
Distributed Caching
If you can't explain when caching is premature, who owns correctness when cache and DB diverge, and what happens during a thundering herd — you're not ready for a Staff design round.
3
Message Queues
Every async system design exposes your understanding of delivery guarantees and failure handling. If you're still saying 'exactly once delivery' in interviews, this playbook will fix that.

Together, these force you to reason about distributed state, failure modes, and ownership tradeoffs — the three dimensions interviewers probe at L6+.

By System Type

Pro

Different interviews stress different system properties. If you know the type of system you'll be asked about, these tracks focus your preparation.

Latency-sensitive
User-facing systems where P99 matters
Data-heavy
Analytical and storage-intensive systems
Correctness-critical
Systems where wrong > slow

Before Your Interview

Quick-reference foundations to scan in 5 minutes. Refresh the mechanics that playbook arguments build on.

Numbers to Know
The 20 latency and throughput numbers you must recall
Consistency Models
What you actually choose during a partition
Caching Fundamentals
Three strategies, three consistency profiles

Key Technologies

Deep dives into the technologies that power system design answers. Architecture, internals, failure modes, and interview-specific application.

Databases
RedisFree
In-memory data store for caching, pub/sub, and leaderboards
PostgreSQLFree
ACID transactions, MVCC, and the default relational database
ElasticsearchFree
Full-text search, log aggregation, and relevance ranking
CassandraFree
Wide-column NoSQL for massive write throughput and multi-DC
DynamoDB
AWS managed NoSQL with single-table design and auto-scaling
Time Series DBs
Prometheus, InfluxDB, TimescaleDB for metrics and telemetry
Messaging
Apache KafkaFree
Distributed event streaming for high-throughput messaging and pipelines
Compute
Flink & Stream Processing
Stateful stream processing with exactly-once and windowing
Infrastructure
API GatewaysFree
Kong, Envoy, NGINX — routing, auth, and rate limiting at the edge
ZooKeeper & etcd
Consensus primitives for leader election and coordination

How to use StaffSignal

  • 1.Pick one playbook from the sidebar. Read it end-to-end in Full Study mode — every section reinforces the others.
  • 2.Do the drills at the end. They're not optional — the drills are where calibration happens.
  • 3.Before your interview, scan the relevant foundation card. Then re-read the playbook's executive summary in Quick Scan mode.

Most candidates study 3–5 playbooks deeply. That's enough.