Add up serial stage latencies against a target (share per stage, slack, bottlene...

{ "method": "GET", "queryParams": { "fanOut": 100, "stages": "dns:20,tls:40,app:120,db:60", "targetMs": 300 }, "type": "http" }

{ "example": { "asOf": "2026-10-11T20:19:39.450Z", "bottleneck": "app", "degraded": false, "disclaimer": "Screening signal computed from the named public source. Not financial, legal or investment advice; provided as is. Verify at the source before acting.", "fanOut": { "calls": 100, "note": "to have 99% of requests entirely within the per-call latency, each call must meet its target 99.9900% of the time", "perCallPercentile": 99, "perCallPercentileNeededForSameOverall": 99.98995016917583, "probabilityAtLeastOneCallSlowerThanItsPercentile": 0.6339676587267709, "requestsHitByTailPercent": 63.3968 }, "notChecked": [ "the distribution of each stage: adding percentiles of stages (p99 + p99) overstates the p99 of the sum, but adding means is exact", "queueing delay under load (see /queue-model) and retries", "…1 more" ], "reasons": [ "Serial stages add; the share column shows where to optimise first.", "Tail amplification: with N parallel calls the chance that at least one is slower than its p99 is 1 - 0.99^N (63% for N = 100), so the request is as slow as its slowest call." ], "serialTotalMs": 240, "slackMs": 60, "source": "computed locally", "stages": [ { "ms": 20, "sharePercent": 8.33, "stage": "dns" }, { "ms": 40, "sharePercent": 16.67, "stage": "tls" } ], "summary": "Serial total 240 ms; biggest stage app (50%). Within the 300 ms target with 60 ms to spare. Fan-out 100 calls at p99: 63.4% of requests see at least one slow call.", "targetMs": 300, "targetUsedPercent": 80, "verdict": "WITHIN_TARGET" }, "type": "json" }