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check_html — HTTP/HTTPS Inspection & Content Validation Tool

Python Version License Status Nagios Plugin NMS_Tools

check_html.py is a deterministic HTTP/HTTPS inspection tool designed for monitoring environments. It performs endpoint validation, backend fingerprinting, and content checks while producing clean, predictable output across JSON, verbose, quiet, and Nagios/Icinga modes.

Features

  • Deterministic HTTP/HTTPS request pipeline with TLS awareness
  • Status code validation (--expect-status)
  • Content-Type validation (--expect-type)
  • Optional HTML body presence validation (--require-html)
  • Backend fingerprinting (headers, banners, HTML signatures)
  • Stable JSON schema for automation
  • Clean, noise‑free CLI parser
  • Nagios/Icinga‑compatible exit codes and perfdata
  • Fast, dependency‑light implementation

Installation

check_html.py requires:

  • Python 3.6+
  • requests library

Install dependencies:

pip install requests

The tool is standalone and does not require system packages or external binaries.

Usage

Basic usage:

./check_html.py -H <host>

Common options:

-H, --host           Target hostname or IP
-p, --port           Port (default: 80 or 443 based on scheme)
--http               Force HTTP
--https              Force HTTPS
-j, --json           Output JSON
-v, --verbose        Verbose diagnostic output
-q, --quiet          Suppress all stdout (exit code only)
--timeout            Connection timeout (default: 5s)
--expect-status      Expected HTTP status code (e.g., 200)
--expect-type        Expected Content-Type (e.g., text/html)
--require-html       Require HTML content in the response body
--require-backend    Require detected backend (e.g., nginx)
--log-dir            Enable logging (disabled in Nagios mode)

Nagios/Icinga mode (default) produces a single deterministic line:

OK - 200 OK (text/html) | latency=0.0012s;;; size=331B;;;

Output Modes

check_html.py has four mutually exclusive output modes:

Nagios/Icinga Mode (default)

  • Activated when no other mode is selected
  • Prints exactly one clean line
  • Never writes logs (even if --log-dir is provided)
  • Designed for deterministic plugin behavior

JSON Mode (-j)

Machine‑readable structured output including:

  • meta (mode, timestamp, logging state)
  • capture (status, headers, content type, body, timing, redirects)
  • backend detection
  • enforcement results
  • perfdata
  • final merged status

Verbose Mode (-v)

Human‑readable diagnostic report including:

  • connection details
  • TLS session (if HTTPS)
  • headers
  • backend detection
  • enforcement summary
  • final result

Quiet Mode (-q)

  • Prints nothing
  • Performs full enforcement internally
  • Returns the correct Nagios exit code
  • Logging is allowed if --log-dir is provided

Enforcement Model

check_html.py applies deterministic validation rules:

  • Status Enforcement — validates status code and expected value
  • Content-Type Enforcement — validates presence and expected type
  • HTML Enforcement — validates HTML body when required
  • Backend Enforcement — fingerprints server backend and validates expectations

Nagios severity precedence:

CRITICAL > WARNING > UNKNOWN > OK

Perfdata

Perfdata fields include:

  • latency — response time
  • size — body size in bytes
  • warn_rt, crit_rt — latency thresholds
  • warn_size, crit_size — size thresholds

Perfdata is included in:

  • Nagios/Icinga mode
  • Verbose mode
  • JSON mode

Not included in Quiet mode (no output).

Exit Codes

Code Meaning
0 OK
1 WARNING
2 CRITICAL
3 UNKNOWN

Exit codes are determined by merged enforcement results.

License

This tool is part of the NMS_Tools suite. See the root project for licensing, documentation, and contributor guidelines.