Delayt

API latency testing with percentile analysis (p50, p95, p99)

Live app: delayt.foo · Docs: delayt.foo/docs

Sequential HTTP requests. Percentile output. Web app for quick runs (≤20 requests); CLI for CI and longer samples.

Why Delayt?

The problem with averages:

Your API might show 50ms average while a few requests take seconds. One slow outlier barely moves the average.

What percentiles tell you:

Metric	Meaning	Why it matters
p50	50% of requests are faster	Median latency in the sample
p95	95% of requests are faster	Common SLO / regression line
p99	99% of requests are faster	Slow tail: spikes and cold starts

If your API shows: avg: 50ms | p95: 500ms | p99: 2000ms

Then 5% of requests in that sample were slower than 500ms, and 1% were slower than 2s. Averages hide that.

Use cases

• Pre-deploy staging check — run against staging before you merge or ship
• Regression testing — same endpoint, same -n, compare p95 before and after a change
• Competitive benchmarking — hit two URLs side by side and compare tails, not averages
• CI gates — fail the build when --assert-p95 exceeds your budget
• Share with the team — web runs get a /r/slug link; CLI supports --share

Quick Start

CLI (no database)

npx @delayt/cli run -u https://api.example.com/health -n 50

# Install globally
npm install -g @delayt/cli
delayt run -u https://api.example.com/health -n 50 --assert-p95=500

Web dashboard caps at 20 requests per endpoint. Use the CLI for 50–200 requests and stable p95/p99.

Web app (local)

git clone https://github.com/devleo10/delayt
cd delayt

docker compose up -d        # PostgreSQL for run history + share links
npm install
npm run build:shared
cp app/.env.example app/.env
npm run dev                 # http://localhost:3000

Open http://localhost:3000 for the landing page, /app for the dashboard.

CI/CD

GitHub Actions

- name: API latency gate
  run: |
    npx @delayt/cli@latest run \
      -u ${{ secrets.STAGING_HEALTH_URL }} \
      -n 50 \
      --assert-p95=500 \
      -q -o json

GitLab CI

latency_smoke:
  image: node:20
  script:
    - npx @delayt/cli@latest run -u "$STAGING_HEALTH_URL" -n 50 --assert-p95=500 -q -o json

Pick --assert-p95 / --assert-p99 for your API. Exit codes: 0 pass · 1 assertion failed · 2 error.

Upload results to the dashboard:

DELAYT_SHARE_URL=https://www.delayt.foo npx @delayt/cli run -u https://api.example.com/health -n 50 --share

Architecture

delayt/
├── app/                # Next.js (App Router): frontend + API
│   ├── src/app/api/    # REST routes
│   ├── src/components/ # Dashboard, charts, share card
│   └── src/lib/        # Runner, analytics, Postgres
├── packages/
│   ├── shared/         # @delayt/shared
│   └── cli/            # @delayt/cli (npm)
└── docker-compose.yml  # Local Postgres

API Reference

POST /api/run

curl -X POST http://localhost:3000/api/run \
  -H "Content-Type: application/json" \
  -d '{
    "endpoints": [{"url": "https://api.example.com/users", "method": "GET"}],
    "requestCount": 15
  }'

Web runs: default 15, max 20 requests per endpoint.

GET /api/run/:id · GET /api/runs · GET /api/share/:slug

See delayt.foo/docs for full API and auth notes.

Development

Command	Description
npm run dev	Next.js dev server
npm run build	Production build (shared + CLI + app)
npm run typecheck	Type-check all packages
npm run test:shared	Shared package unit tests
npm run cli -- run -u URL -n 10	Run CLI from source

Env: copy app/.env.example → app/.env. Requires DATABASE_URL for run history and share links.

Links

• App: delayt.foo
• Repo: github.com/devleo10/delayt
• CLI on npm: @delayt/cli
• Author: @_devleo10

If this helps, star the repo.

License

MIT © 2026