Local engine
inference calculator
KV Cache Calculator
Watch context length turn into GPU memory: layers, KV heads, precision, tokens, and batch, live.
Why do long context and batch size compete for the same GPU?
Open KV Cache Calculator
Fanout Labs · directory
Technical systems you can touch.
Explore real calculators, parsers, simulations, live-data tools, model evaluations, interviews, and games across AI and systems.
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111 matches · 107 local · 4 model · 0 coming soon
Local engine
inference calculator
GPU Model Fit
Multiply parameters by precision bytes, add runtime overhead, and see which cards say yes.
Does this checkpoint actually fit on that GPU?
Open GPU Model Fit
Local engine
inference calculator
Latency Numbers Every Engineer Should Know
Compose a request out of classic latency numbers and watch the budget disappear op by op.
Which operation dominates this request's budget?
Open Latency Numbers Every Engineer Should Know
Local engine
inference calculator
Quantization Microscope
Slide the bit-width and watch weights shrink, decode speed rise, and quality risk creep in.
What does dropping from 16 to 4 bits actually buy?
Open Quantization Microscope
Local engine
inference calculator
Back-of-the-Envelope Estimator
Turn QPS, fan-out, and per-request cost into a defensible capacity number.
How many servers does this traffic estimate really need?
Open Back-of-the-Envelope Estimator
Local engine
inference calculator
LLM Serving Architect
Turn measured throughput numbers into a fleet layout for a serving stack.
Prefill, decode, or memory — what binds this deployment first?
Open LLM Serving Architect
Local engine
inference simulation
Speculative Decoding Race
Race draft-and-verify decoding against plain decoding across acceptance rates.
How often must the draft model agree for speculation to win?
Open Speculative Decoding Race
Local engine
inference simulation
Continuous Batching Dispatcher
Schedule sequences into decode slots and watch padding waste fall away.
Why does continuous batching lift GPU utilization?
Open Continuous Batching Dispatcher
Local engine
inference calculator
Prefill–Decode Roofline
Plot the two inference phases against a roofline and read off the regime.
Are you compute-bound or bandwidth-bound at this context length?
Open Prefill–Decode Roofline
Local engine
inference calculator
Prompt Cache Savings Planner
Model shared system prompts as cached tokens and total the savings.
How much do reused prefixes shave off the bill?
Open Prompt Cache Savings Planner
Local engine
inference calculator
Multi-GPU Parallelism Mapper
Map a model's layers and activations onto parallel strategies and compare memory.
Tensor, pipeline, or data parallel for this shape of model?
Open Multi-GPU Parallelism Mapper
Local engine
ai game
MoE Routing Arcade
Route tokens across experts under a capacity constraint and keep the load even.
Can you balance the experts before one melts down?
Open MoE Routing Arcade
Local engine
system design simulation
Queue Capacity & Backpressure Lab
Push producers faster than consumers and watch queues, waits, and drops emerge.
At what queue depth does the consumer tip over?
Open Queue Capacity & Backpressure Lab
Local engine
system design simulation
Rate Limiter Studio
Run an exact token-bucket trace to see burst admission, refill, and the first rejection.
Which requests does this token-bucket policy admit or reject?
Open Rate Limiter Studio
Local engine
system design simulation
Retry & Jitter Studio
Measure retry amplification, then spread it back out with backoff and jitter.
What do three retries really do to the dependency's load?
Open Retry & Jitter Studio
Local engine
system design simulation
Consistent Hash Ring Studio
Add and remove ring nodes, with and without virtual nodes, and count migrating keys.
How many keys actually move when a node leaves?
Open Consistent Hash Ring Studio
Local engine
system design calculator
Bloom Filter Tuner
Size the bit array and hash count for your error budget — and watch the trade curve.
How many bits buy the false-positive rate you need?
Open Bloom Filter Tuner
Local engine
system design calculator
Tail Latency Fan-Out Simulator
Fan a request out to N leaves and watch the tail stretch; then try hedged requests.
Why does one slow leaf decide the request's p99?
Open Tail Latency Fan-Out Simulator
Local engine
system design simulation
Architecture Bottleneck Simulator
Propagate traffic math through a service graph and expose the capacity cliff.
Which dependency reaches instability first as traffic grows?
Open Architecture Bottleneck Simulator
Local engine
system design calculator
Timeout Architect
Assign per-hop timeouts so the slowest dependency fails fast instead of dragging everything.
Where should each timeout sit along this call chain?
Open Timeout Architect
Local engine
system design simulation
Circuit Breaker State Machine
Drive failures through a breaker and watch closed/open/half-open transitions.
When does the breaker flip — and when should it half-open?
Open Circuit Breaker State Machine
Local engine
system design simulation
Cache Stampede Lab
Expire a hot key under load and compare naive, lock, and jittered-TTL strategies.
How bad is expiry thundering-herd at this TTL?
Open Cache Stampede Lab
Local engine
system design simulation
Retry Storm Cascade
Multiply per-hop retries down a call chain and then break the cascade correctly.
How does a 2x retry policy become 16x at four hops?
Open Retry Storm Cascade
Local engine
system design simulation
Autoscaling Lag Simulator
Watch demand jump, cooldowns delay capacity, and the backlog queue drain late.
How long is your fleet undersized after the spike?
Open Autoscaling Lag Simulator
Local engine
system design game
Load Balancer Algorithm Race
Race balancing algorithms against a mixed workload and read the queue depth.
Round-robin or least-connections under uneven request costs?
Open Load Balancer Algorithm Race
Local engine
system design game
CDN Cache-Key Debugger
Inspect cache keys across variants and find the poisoning parameter.
Which header quietly split your cache?
Open CDN Cache-Key Debugger
Local engine
system design calculator
Shard-Key Heatmap
Distribute keys by hash and by range and watch the hot shard glow.
How skewed is celebrity data across 16 shards?
Open Shard-Key Heatmap
Local engine
system design simulation
Cache Working-Set Simulator
Push a skewed stream through LRU/LFU/ARC and read hit rate against cache size.
What hit rate does this LRU hold under Zipf traffic?
Open Cache Working-Set Simulator
Local engine
system design game
HTTP Protocol Waterfall Race
Waterfall the same page over 1.1/2/3 and count the round trips.
What does HTTP/2 multiplexing actually save on 30 assets?
Open HTTP Protocol Waterfall Race
Local engine
system design simulation
DNS Resolution Journey
Follow a cold lookup end to end, then make TTL caching erase the hops.
Root, TLD, authoritative — how many hops is one lookup?
Open DNS Resolution Journey
Local engine
system design game
Jepsen History Inspector
Re-order concurrent operations and judge which interleavings hold.
Is this history linearizable?
Open Jepsen History Inspector
Local engine
system design game
Multi-Region Failover Game
Play the incident — drain, promote, and watch RTO tick down.
Can you fail over before the error budget burns?
Open Multi-Region Failover Game
Local engine
system design calculator
Cloud Unit Economics Canvas
Decompose compute, storage, and egress into a per-request unit cost.
What does one request cost at this scale?
Open Cloud Unit Economics Canvas
Local engine
system design calculator
Kubernetes Resource Rightsizer
Set CPU/memory requests from percentile usage and stop funding idle capacity.
Are these requests oversized by 4x again?
Open Kubernetes Resource Rightsizer
Local engine
system design calculator
Connection Pool Sizer
Little's Law meets max_connections: size pools that neither queue nor crush the DB.
How big should the pool be — and what breaks when it's bigger?
Open Connection Pool Sizer
Local engine
system design calculator
Storage Growth & Retention Planner
Project ingest and retention policies into a growth curve with prices attached.
When does this table hit 10 TB — and can you afford it?
Open Storage Growth & Retention Planner
Local engine
system design calculator
CIDR & Subnet Canvas
Split address space visually and read the host math off each block.
Carve a /16 into prod, staging, and data — without waste.
Open CIDR & Subnet Canvas
Local engine
system design simulation
CORS Request Explainer
Walk through simple vs preflighted requests and the headers that decide.
Why did this request preflight but that one didn't?
Open CORS Request Explainer
Local engine
system design simulation
Raft Election & Log Lab
Step through terms, votes, and log-matching rules by hand.
Why can't a stale candidate win the election?
Open Raft Election & Log Lab
Local engine
system design game
CAP Partition Game
Play both sides of the tradeoff and feel why 'CA' isn't on the menu.
Partition hits: serve possibly-stale reads or refuse them?
Open CAP Partition Game
Local engine
system design game
CRDT Merge Desk
Play with counters, sets, and registers that always converge.
Can you merge without a leader and lose no writes?
Open CRDT Merge Desk
Local engine
system design simulation
Kafka Partition & Consumer Lab
Partition a topic, size a consumer group, and watch ordering constraints bind.
Why does consumer #9 sit idle while the lag grows?
Open Kafka Partition & Consumer Lab
Local engine
system design simulation
Saga Timeline Designer
Line up steps and compensations and read the rollback timeline.
Your payment step failed at T+3 — what unwinds?
Open Saga Timeline Designer
Local engine
system design game
Deadlock Graph Builder
Build the waits-for graph and find the cycle before the database does.
Can you close the cycle that deadlocks the system?
Open Deadlock Graph Builder
Local engine
system design calculator
Postgres EXPLAIN Lens
Feed cardinality through planner-ish cost math and predict the plan.
Seq scan or index — what does the planner see?
Open Postgres EXPLAIN Lens
Local engine
system design calculator
Query Plan Diff
Diff two plans side by side and find the row-estimate lie.
What changed between yesterday's plan and today's regression?
Open Query Plan Diff
Local engine
system design simulation
B+ Tree Index Playground
Insert, split, and look up in a live B+ tree drawing.
How many pages does a point lookup touch?
Open B+ Tree Index Playground
Local engine
system design simulation
LSM Compaction Visualizer
Flush memtables, merge levels, and watch write amplification stack up.
Why do reads spike during compaction storms?
Open LSM Compaction Visualizer
Local engine
system design simulation
Transaction Isolation Anomaly Lab
Interleave two transactions and watch dirty and non-repeatable reads appear.
Which anomalies exist at read committed?
Open Transaction Isolation Anomaly Lab
Local engine
system design studio
API Contract Studio
Edit a contract and run compatibility checks against recorded consumers.
Does this response change break anyone's client?
Open API Contract Studio
Local engine
agents simulation
Agent Trace Replay
Replay model/tool spans on a timeline with latency, errors, and concurrency.
Where did time and failure accumulate in this agent trace?
Open Agent Trace Replay
Local engine
agents studio
Tool Mock Server
Serve canned success/timeout/error variants and watch the loop cope.
What does your agent do when the tool 500s?
Open Tool Mock Server
Local engine
agents game
Agent Loop Escape Room
Debug runaway agent loops shaped by bad fallbacks and missing stop words.
The loop keeps calling the same tool — can you break it?
Open Agent Loop Escape Room
Local engine
agents calculator
Tool-Choice Confusion Matrix
Count chosen vs intended tools across prompts and plot the confusion.
Which two tools does the model keep swapping?
Open Tool-Choice Confusion Matrix
Local engine
agents studio
Webhook Inspector & Replayer
Capture webhook payloads, edit, and replay them against your handler.
What did that delivery actually contain?
Open Webhook Inspector & Replayer
Local engine
ai game
Long-Context Needle Hunt
Plant needles at depths in a synthetic context and map recall by position.
Does the model find the fact at 15% or 85% of context?
Open Long-Context Needle Hunt
Local engine
ai studio
Reranker Workbench
Blend lexical and embedding scores and watch the top-20 reshuffle.
Which candidate deserves rank 1 — semantic or BM25?
Open Reranker Workbench
Local engine
ai simulation
GraphRAG Path Explorer
Traverse an entity graph to the evidence nodes a GraphRAG query needs.
Which subgraph should this question even touch?
Open GraphRAG Path Explorer
Local engine
agents studio
PDF-to-RAG Readiness Scan
Score a PDF's layout for extraction risk before it poisons the index.
Is this document chunkable — or a table soup?
Open PDF-to-RAG Readiness Scan
Local engine
ai studio
RAG Chunking Workbench
Chunk a sample corpus three ways and grade retrieval by boundary quality.
Fixed, recursive, or semantic — where do boundaries hurt least?
Open RAG Chunking Workbench
Local engine
agents studio
RAG Failure Debugger
Isolate the failing stage with staged captures from a real-style pipeline.
Was it retrieval, reranking, or generation that failed?
Open RAG Failure Debugger
Local engine
ai calculator
Hybrid Search Mixer
Fuse two ranked lists with a weighted mixer and see where each shines.
What alpha blends BM25 and vectors best for this query?
Open Hybrid Search Mixer
Local engine
ai calculator
Retrieval Threshold Tuner
Slide the similarity threshold across a scored corpus and trace the F1 curve.
Recall at 90% — what does the precision cost?
Open Retrieval Threshold Tuner
Local engine
research studio
Eval Leakage & Dedup Scanner
Hunt near-duplicates across splits with n-gram overlap heuristics.
Is your test set inside the training set?
Open Eval Leakage & Dedup Scanner
Local engine
agents studio
MCP Inspector Lite
Walk a mock server's capabilities, schemas, and permission surface.
Which tools does this MCP server really expose?
Open MCP Inspector Lite
Local engine
ai simulation
Attention Atlas
Paint per-head patterns from a small attention trace and name the behaviors.
Which head is doing induction — and which is noise?
Open Attention Atlas
Local engine
ai simulation
Embedding Galaxy
Fly through a projected embedding space and stress-test your distance intuition.
What does 'nearest' mean in 1536 dimensions?
Open Embedding Galaxy
Local engine
prompting game
Prompt Gauntlet
Harden a system prompt against drift, injection, and verbosity creep.
Can you keep the format under adversarial inputs?
Open Prompt Gauntlet
Local engine
prompting studio
Prompt Linter
Lint prompt text for ambiguity, conflicts, stale rules, and token waste.
Which words in this prompt are doing nothing?
Open Prompt Linter
Local engine
prompting studio
Structured Output Schema Studio
Tune schema strictness and instructions until the output validates clean.
Why does the model keep adding prose around your JSON?
Open Structured Output Schema Studio
Local engine
prompting studio
JSON Repair & Formatter
Repair classic model JSON injuries: trailing commas, comments, cut tails.
Can you salvage the missing-brace response?
Open JSON Repair & Formatter
Local engine
prompting studio
System Prompt Conflict Map
Stack role, style, format, and safety rules and surface their collisions.
Which two of your rules contradict each other?
Open System Prompt Conflict Map
Needs model key
prompting studio
Prompt Batch Runner
Diff two prompts across a small suite and score structured wins/losses.
Does the new prompt beat the old one on 30 cases?
Open Prompt Batch Runner
Local engine
prompting game
Prompt Injection Firewall
Grade wrapped inputs and watch which delimiters leak instructions.
Spot the payload hiding in the 'user data'.
Open Prompt Injection Firewall
Needs model key
prompting game
Pairwise Preference Arena
Run blind pairwise judging and watch judge bias appear in real time.
A or B — and would you bet your eval on it?
Open Pairwise Preference Arena
Local engine
research studio
Canary Benchmark Builder
Assemble minimal canary suites with stratified coverage.
Which 20 questions catch this regression earliest?
Open Canary Benchmark Builder
Local engine
prompting studio
Model Migration Regression Dashboard
Compare before/after runs across categories and gate the migration.
What broke when you moved providers?
Open Model Migration Regression Dashboard
Local engine
prompting studio
Prompt Diff & Regression Grid
Grid outputs across prompt versions and flag behavioral drift.
Line by line, what did prompt v7 change?
Open Prompt Diff & Regression Grid
Local engine
prompting studio
Few-Shot Example Curator
Pick demonstrations by coverage and watch format adherence jump.
Which three examples teach this format best?
Open Few-Shot Example Curator
Local engine
prompting studio
Model Response Comparator
Line up responses side by side with rubric scoring.
Same prompt, three models — grade the spread.
Open Model Response Comparator
Needs model key
prompting studio
LLM Judge Calibration Studio
Calibrate a judge's rubric against a labeled set and watch agreement move.
How far is your judge from human labels?
Open LLM Judge Calibration Studio
Local engine
research studio
Failure Taxonomy Builder
Cluster failures into a taxonomy you can actually drive fixes from.
Can you name the five ways this system fails?
Open Failure Taxonomy Builder
Local engine
research studio
Safety Policy Test Matrix
Exercise intent × content grids and find the uncovered cells.
Does the policy surface hold across the matrix?
Open Safety Policy Test Matrix
Local engine
research calculator
Bias Slice Explorer
Split an eval by attribute slices and compare deltas like an auditor.
Does accuracy hold across the slices you care about?
Open Bias Slice Explorer
Local engine
research studio
Research Gap Radar
Scan a draft for unsupported claims and missing baselines.
Which of these claims lacks a citation?
Open Research Gap Radar
Local engine
research studio
Paper-to-Code Repro Checker
Score a paper's reproducibility surface: code, seeds, splits, configs.
Is this result reproducible from what's published?
Open Paper-to-Code Repro Checker
Local engine
research studio
Experiment Design Copilot
Structure variables, controls, and readouts before GPU-hours burn.
One variable at a time — does your design have it?
Open Experiment Design Copilot
Local engine
research studio
Literature Comparison Matrix
Grid papers against method, data, scale, and result to expose overlap.
Six papers, four axes — where's the real delta?
Open Literature Comparison Matrix
Local engine
research studio
Figure & Equation Explainer
Annotate dense paper artifacts into plain-language readings.
What is equation (4) actually saying?
Open Figure & Equation Explainer
Needs model key
research game
AI Research Interview Simulator
A mock loop of depth-first questioning on a paper you claim to know.
Can you defend the method section cold?
Open AI Research Interview Simulator
Local engine
research game
AI System Design Mock Interview
Timed prompting with probes that push past your first architecture.
Design a feature-store platform in 40 minutes — go.
Open AI System Design Mock Interview
Local engine
ops calculator
Error Budget & Burn Rate Planner
Budget math made visible: windows, multipliers, and paging triggers.
How many bad minutes remain before the page?
Open Error Budget & Burn Rate Planner
Local engine
ops studio
Study Daily Planner
Block a realistic study session with spaced-repetition smarts.
Can you fit papers, labs, and notes into 90 focused minutes?
Open Study Daily Planner
Local engine
ai calculator
Eval Confidence Interval Lab
Put binomial confidence intervals on leaderboard deltas before believing them.
Is 84.2% on 100 items actually better than 82%?
Open Eval Confidence Interval Lab
Local engine
ai simulation
How AI Remembers
Walk weights, context, cache, RAG, and profiles with live mini-demos.
Five kinds of 'memory' — which one is doing this?
Open How AI Remembers
Local engine
agents studio
Repo-to-System Map
Map a repository's modules into a first-guess system diagram.
What architecture hides inside this dependency graph?
Open Repo-to-System Map
Local engine
agents studio
Architecture Diagram Reviewer
Check a diagram for missing arrows, silent dependencies, and vague boxes.
What is this diagram not telling the reviewer?
Open Architecture Diagram Reviewer
Local engine
research studio
Citation Coverage River
Flow claims to citations and measure support by stream width.
How much of the argument does the evidence carry?
Open Citation Coverage River
Local engine
research studio
Claim-to-Citation Matrix
Matrix claims against citations and expose the unsupported assertions.
Every claim to a source — where are the orphans?
Open Claim-to-Citation Matrix
Local engine
research simulation
Paper Galaxy
Orbit a topic's key papers by year, venue, and citation pull.
Where does this paper sit in the citation cosmos?
Open Paper Galaxy
Local engine
research studio
Daily Paper Radar
Score the feed by relevance and novelty and build the reading queue.
Which of today's 200 uploads is worth 15 minutes?
Open Daily Paper Radar
Local engine
research studio
Ablation Planner
Design the ablation grid that isolates each contribution cleanly.
Which components earn their keep — prove it.
Open Ablation Planner
Local engine
research game
Reproduction Sprint
Sequence environment, data, training, and eval against the clock.
Seven days to reproduce the headline number — plan it.
Open Reproduction Sprint
Local engine
ops game
Incident Commander Simulation
Run a live incident: triage, mitigate, communicate, and review.
Traffic up, p99 red, slack pinging — command it.
Open Incident Commander Simulation
Local engine
agents game
Agent Control Room
Supervise fleets: spot loops, cap runaways, and requeue work.
Six agents live — which one is burning the budget?
Open Agent Control Room
Local engine
prompting studio
AI Input Privacy Scrubber
Pattern-scan inputs for keys, PII, and customer data before they leave.
Did that prompt just leak a secret?
Open AI Input Privacy Scrubber
Local engine
agents studio
MCP Permission Risk Map
Map tool scopes to risk tiers and draw the least-privilege line.
What could this tool do with your credentials?
Open MCP Permission Risk Map
Local engine
math simulation
Gradient Descent Visualizer
Step descent down a loss surface you can see: lr, steps, and the where-it-lands trace.
Why does a big learning rate bounce out of the ravine?
Open Gradient Descent Visualizer
Local engine
ai studio
Tokenizer Context Playground
Split text into tokens and watch word pieces, whitespace, and unicode add up.
Why does this 'short' prompt cost 4x the tokens?
Open Tokenizer Context Playground
Local engine
ai simulation
Sampling Playground
Shape a mock next-token distribution and sample from it live.
Greedy, top-k, top-p, temperature — what changes first?
Open Sampling Playground
Local engine
inference calculator
Model Router & Pareto Explorer
Plot models on price/quality axes and route each request class to the frontier.
Which model sits on the cost–quality frontier for this traffic?
Open Model Router & Pareto Explorer