Assertwise Lab
Free tools for testers and developers
Eleven practical tools from our day-to-day testing work: quick checks for your API's latency, security headers, TLS and rate limits; generators and calculators for k6, capacity and SLOs; and templates for test plans and launches. Some run in your browser, others on our server. See each tool for details.
SERVERPerformance & load
API response time check
Up to 10 sequential GETs with DNS, TCP, TLS, TTFB and total time, p50/p95 and status codes.
Why: See where latency comes from before you load test.
Open tool →SERVERSecurity
Security headers & CORS check
Grades HSTS, CSP, X-Content-Type-Options, frame options, Referrer- and Permissions-Policy, cookies and CORS.
Why: Catch reflected-origin CORS and missing headers in one minute.
Open tool →SERVERSecurity
SSL/TLS certificate check
Expiry, issuer, SAN match, chain validation, negotiated protocol and cipher, TLS 1.0/1.1 acceptance.
Why: Avoid expired certs and broken chains in production.
Open tool →SERVERSecurity
Rate-limit indicator
Up to 10 quick requests; detects 429 and RateLimit, X-RateLimit and Retry-After headers.
Why: A light first signal for OWASP API4 – not a load test.
Open tool →IN-BROWSERAPI design
OpenAPI validator & linter
Validates OpenAPI 3.x (YAML/JSON): schema errors, unresolved $refs, docs, naming, auth and OWASP API Top 10 hints.
Why: Find missing 401/403/429 and pagination limits before pentesters do.
Open tool →IN-BROWSERPerformance & load
k6 script generator
Turns an OpenAPI spec or a curl command into a k6 script with scenarios, thresholds and checks.
Why: Go from spec to first load test in minutes.
Open tool →IN-BROWSERPerformance & load
Capacity calculator (Little's Law)
Concurrent users, think time and response time → RPS, concurrency, per-instance load and DB pool size.
Why: Size your load test and connection pools with real math.
Open tool →IN-BROWSERReliability / SRE
SLO & error budget calculator
Availability target → allowed downtime per day, week, month, quarter, year, plus burn-rate alert thresholds.
Why: Know what 99.9% really means and alert on budget burn, not noise.
Open tool →IN-BROWSERPerformance & load
k6 / JMeter results analyzer
Upload k6 JSON or summary exports or JMeter JTL CSV: percentiles, throughput over time, errors, charts and an automatic summary.
Why: Turn raw results into a summary your team can act on.
Open tool →SERVERQA & templates
AI test case generator
Paste a user story or endpoint description and get positive, negative, edge and security test cases. Export as Markdown or CSV.
Why: A strong first draft for your test suite in seconds.
Open tool →IN-BROWSERQA & templates
Free testing templates (PDF)
Pre-launch readiness checklist, test plan template and fintech API testing checklist – in English and German.
Why: Proven structure from real engagements, free to use.
Open tool →Server-side checks send a few light requests to the target you enter, only after you confirm you are authorized. Details in our privacy policy.
Want a senior engineer to look at the results?
Free tools give you a first signal. In a free 20-minute check-up we review your API, performance or test setup and tell you what to fix first.