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 Coming soon
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.
Need full test management next?
Assertwise TestHub is in early access — EU-hosted suites, runs and imports for QA teams.
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.