# API Latency Budget Planner Plan and visualise an API latency budget. Enter a P99 target (e.g. ≤ 300ms) and per-stage allocations (DNS, TCP, TLS, TTFB, Processing, Network) to see a live waterfall, budget utilisation, and over-budget warnings. Optionally paste an OpenTelemetry or Datadog trace to reverse-engineer a measured allocation. > Canonical page: https://elysiatools.com/en/tools/api-latency-budget-planner - **Category:** Development - **Keywords:** latency budget, slo, p99, waterfall, opentelemetry, datadog, trace, performance budget, api, ttfb, request stages, sre, observability, apm ## Overview An SLO / performance-budget planner for SREs and API designers: 1. **Total budget** — set the P99 target (e.g. 300ms). Optionally pick a service-level objective label (P50/P90/P99/P99.9) shown in the summary. 2. **Stage allocation** — list each request stage and its budgeted milliseconds, one per line, e.g. `DNS=5`, `TLS=20`, `TTFB=80`, `Processing=120`. 3. **Waterfall** — a colour-coded bar chart shows each stage's share of the budget. Stages over a 35% soft cap are flagged red. 4. **Headroom & over-budget** — the summary reports how much budget is used and whether you are within or over the target, with a proportional reallocation suggestion. 5. **Trace import** — paste an OpenTelemetry or Datadog trace (JSON) and the tool extracts per-span durations, buckets by name, and suggests an initial allocation derived from real measurements. All computation runs locally in the browser. ## Inputs - **Total latency budget (P99, ms)** (number): The overall latency target in milliseconds (e.g. 300 for P99 ≤ 300ms). - **Stage allocation (name=ms, one per line)** (textarea): One stage per line as name=ms (also accepts name: ms or name ms). - **Service-level objective** (select) - **Paste trace (OpenTelemetry / Datadog JSON, optional)** (textarea): Optional OpenTelemetry or Datadog trace JSON. The tool extracts per-span durations to suggest an allocation. ## When to use - Designing a new microservice API and establishing latency SLO targets for individual network and processing stages. - Debugging an API that is exceeding its P99 latency budget and needing to identify which stage is consuming the most headroom. - Translating raw OpenTelemetry or Datadog trace spans into a structured, visual latency budget for team alignment. ## How it works - Set your total latency budget target in milliseconds and select your target service-level objective (such as P50, P90, or P99). - Enter your stage allocations (e.g., DNS, TCP, TLS, TTFB, Processing, Network) using the name=ms format, one per line. - Optionally paste an OpenTelemetry or Datadog trace JSON to extract real span durations and compare them against your budget. - Review the live waterfall chart, budget utilization summary, and warnings for any stages exceeding the 35% soft cap. ## Use cases - Establishing baseline latency budgets for multi-region API gateways during the architecture phase. - Analyzing production performance bottlenecks by comparing Datadog trace JSONs against target SLOs. - Proportionally reallocating latency budgets for downstream microservices when upstream processing times increase. ## Frequently asked questions ### What is an API latency budget? It is the allocation of maximum allowable response times across different stages of an API request (like DNS lookup, TLS handshake, and database processing) to meet an overall SLO target. ### How does the trace import feature work? You can paste a JSON trace from OpenTelemetry or Datadog. The tool parses the span durations, groups them by name, and suggests a baseline allocation based on those real measurements. ### Why are some stages highlighted in red in the waterfall chart? Stages that consume more than 35% of the total latency budget are flagged with a red warning to highlight potential performance bottlenecks. ### What happens if my allocations exceed the total budget? The planner displays an over-budget warning, calculates the excess milliseconds, and suggests a proportional reallocation to bring the stages back within the target. ### Is my trace data sent to any external servers? 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