# testssl.sh vs SSL Labs: How the Open-Source TLS Scanner Compares to Online Tools > Compare testssl.sh and SSL Labs for TLS testing. Discover how the open-source scanner offers local privacy, custom ports, and CI/CD integration. - Repository: [Dirk Wetter/testssl.sh](https://github.com/drwetter/testssl.sh) - Tags: comparison - Published: 2026-03-01 --- **testssl.sh implements the same SSL Labs Server Rating Guide algorithm locally while offering privacy, custom port scanning, and CI/CD integration that cloud-based scanners cannot match.** When evaluating TLS configurations, security professionals often compare the open-source **testssl.sh** tool against Qualys SSL Labs. While both use identical grading methodologies, the drwetter/testssl.sh repository provides a local Bash implementation that eliminates third-party data exposure and removes network scope restrictions inherent to cloud services. ## Execution Model and Architecture ### Local Bash Script vs Cloud Service testssl.sh operates as a **local Bash script** that drives native OpenSSL binaries and custom socket code directly from your machine. According to the source in [`testssl.sh`](https://github.com/drwetter/testssl.sh/blob/main/testssl.sh) (lines 62-66), the script establishes connections using client-side resources rather than remote infrastructure. SSL Labs, conversely, runs as a cloud service where scans execute on Qualys-controlled servers, requiring you to submit target URLs to external infrastructure. ### Target Scope and Reachability The local execution model enables testssl.sh to scan **any TLS-enabled service** reachable from your client, including HTTPS, SMTP, POP, IMAP, STARTTLS, and custom ports. As documented in [`Readme.md`](https://github.com/drwetter/testssl.sh/blob/main/Readme.md) (lines 24-27), you can point the script at arbitrary hosts, IPs, and non-standard ports. SSL Labs restricts scanning to public web servers on standard ports (443, 8443), excluding internal services or alternative protocols. ## Data Collection and Client Simulation ### OpenSSL and Socket Implementation testssl.sh combines **OpenSSL** for cipher-suite negotiation with a Bash socket implementation for features inaccessible through standard libraries. The architecture described in [`testssl.sh`](https://github.com/drwetter/testssl.sh/blob/main/testssl.sh) (lines 48-56) handles TLS 1.3 early-data and client-hello fingerprints that pure OpenSSL cannot expose. SSL Labs performs equivalent handshake analysis but through proprietary cloud-based scanners with fixed network perspectives. ### Client Simulation Data Sources For browser compatibility testing, testssl.sh pulls **Qualys SSL Labs client simulation data** directly. The script references this data in [`etc/client-simulation.txt`](https://github.com/drwetter/testssl.sh/blob/main/etc/client-simulation.txt), containing browser fingerprints and JA3 hashes sourced from SSL Labs. While SSL Labs embeds this data internally, testssl.sh exposes it locally through the [`utils/update_client_sim_data.pl`](https://github.com/drwetter/testssl.sh/blob/main/utils/update_client_sim_data.pl) utility, allowing offline client simulation without internet dependency during scans. ## Rating Methodology and Grading ### SSL Labs Server Rating Guide Implementation testssl.sh implements a **near-complete copy** of the SSL Labs Server Rating Guide (version 2009r, 2025-05-16). The grading algorithm at [`testssl.sh`](https://github.com/drwetter/testssl.sh/blob/main/testssl.sh) (lines 24147-24153) produces identical A-F grades and exposes underlying score components. SSL Labs applies the same public rating formula, though their online service may incorporate undisclosed heuristics for "overall grade" adjustments that the open-source implementation does not replicate. ## Privacy, Speed, and Extensibility ### Privacy and Data Sovereignty All scan traffic and results remain **on the client machine** when using testssl.sh. The privacy guarantee in [`Readme.md`](https://github.com/drwetter/testssl.sh/blob/main/Readme.md) (lines 39-41) ensures no third party observes your scanned data unless explicitly published. SSL Labs scans expose target server handshake data to Qualys infrastructure, creating potential compliance concerns for sensitive internal assessments. ### Performance and Parallel Processing Running locally eliminates cloud queue delays. testssl.sh supports **parallel mass-testing** through the built-in `--parallel` mode (lines 4444-4450 in [`testssl.sh`](https://github.com/drwetter/testssl.sh/blob/main/testssl.sh)), limited only by client machine resources and network latency. SSL Labs operates through a fixed scanner pool with rate limits and queue-based throughput. ### Customization and CI Integration As open-source Bash code, testssl.sh allows modification of checks, output formats (JSON/CSV/HTML), and integration with CI pipelines. The flexibility noted in [`Readme.md`](https://github.com/drwetter/testssl.sh/blob/main/Readme.md) (line 36) enables automated security regression testing. SSL Labs provides only a closed-source UI and API without internal customization options. ## Practical Usage Examples The following commands demonstrate testssl.sh capabilities unavailable through online scanners: Basic HTTPS scan: ```bash ./testssl.sh https://example.com ``` Non-standard port scanning (SMTP STARTTLS on 587): ```bash ./testssl.sh --starttls smtp -p 587 mail.example.org ``` Machine-readable JSON for CI pipelines: ```bash ./testssl.sh --jsonfile result.json example.com ``` Quick cipher-only assessment: ```bash ./testssl.sh --fast example.com ``` Parallel mass-testing with 10 workers: ```bash ./testssl.sh --parallel 10 --file hostlist.txt ``` These examples derive from the official documentation in [`doc/testssl.1.md`](https://github.com/drwetter/testssl.sh/blob/main/doc/testssl.1.md) (lines 120-140). ## Summary - **testssl.sh** runs locally as a Bash script using OpenSSL and socket implementations, while SSL Labs operates as a proprietary cloud service. - Both tools implement the identical SSL Labs Server Rating Guide (version 2009r) for A-F grading, though testssl.sh exposes the underlying calculation logic in [`testssl.sh`](https://github.com/drwetter/testssl.sh/blob/main/testssl.sh) (lines 24147-24153). - Local execution enables scanning of internal networks, non-standard ports, and non-web protocols like SMTP and IMAP. - Client simulation data originates from the same Qualys source but remains under your control in [`etc/client-simulation.txt`](https://github.com/drwetter/testssl.sh/blob/main/etc/client-simulation.txt). - Privacy-preserving architecture keeps all handshake data on your machine, eliminating third-party exposure. - Parallel processing capabilities (lines 4444-4450) and multiple output formats support enterprise automation and CI/CD workflows. ## Frequently Asked Questions ### Does testssl.sh provide the same grades as SSL Labs? Yes. testssl.sh implements a near-complete copy of the SSL Labs Server Rating Guide (version 2009r, 2025-05-16) as shown in [`testssl.sh`](https://github.com/drwetter/testssl.sh/blob/main/testssl.sh) (lines 24147-24153). The script produces identical A-F letter grades and displays underlying score components. Minor deviations may occur if SSL Labs applies undisclosed heuristics for "overall grade" adjustments. ### Can I use testssl.sh to scan internal servers? Absolutely. Because testssl.sh runs locally from the client machine (lines 62-66 in [`testssl.sh`](https://github.com/drwetter/testssl.sh/blob/main/testssl.sh)), it can reach any TLS-enabled service on your network, including private IPs and non-standard ports. SSL Labs only scans public-facing web servers on standard HTTPS ports. ### How does testssl.sh handle TLS 1.3 testing? testssl.sh uses a hybrid approach combining OpenSSL for standard handshake tests and a custom Bash socket implementation for TLS 1.3-specific features like early-data (0-RTT) that OpenSSL cannot expose. This architecture is documented in [`testssl.sh`](https://github.com/drwetter/testssl.sh/blob/main/testssl.sh) (lines 48-56). ### Is testssl.sh suitable for automated CI/CD pipelines? Yes. The tool supports JSON, CSV, and HTML output formats via command-line flags like `--jsonfile`, enabling automated parsing and regression detection. The open-source Bash implementation allows integration with Jenkins, GitLab CI, or GitHub Actions without API rate limits or external service dependencies.