Keyword Highlighting

Overview

Keyword highlighting automatically colorizes patterns in terminal output (errors, warnings, IP addresses, etc.) to help you quickly identify important information. Netcatty uses xterm.js decorations for zero-performance-impact highlighting.

How It Works

Keyword highlighting operates on visible terminal content:

Pattern Matching: Regular expressions are matched against each line
Lazy Highlighting: Only visible viewport is processed (debounced)
Decorations API: Colors are applied as overlays without modifying data
Auto-disabled in Alternate Buffer: Disabled in vim/htop for performance

Highlighting is purely visual - it doesn’t affect terminal data or command execution.

Highlight Rules

Each rule defines patterns to match and the color to apply.

Rule Structure

KeywordHighlightRule

object

Show Properties

string

required

Unique rule identifier (e.g., error, ip-address)

label

string

required

Display name for the rule (e.g., “Error Messages”)

patterns

string[]

required

Array of regex patterns to match (case-insensitive, global)

color

string

required

Highlight color in hex format (e.g., #F87171)

enabled

boolean

required

Whether this rule is active

Example Rule

{
  "id": "error",
  "label": "Error",
  "patterns": [
    "\\[error\\]",
    "\\[err\\]",
    "\\berror\\b",
    "\\bfail(ed)?\\b",
    "\\bfatal\\b",
    "\\bcritical\\b",
    "\\bexception\\b"
  ],
  "color": "#F87171",
  "enabled": true
}

This rule matches:

[error] or [err] in brackets
The word “error” (whole word)
“fail” or “failed”
“fatal”, “critical”, “exception”

Default Highlight Rules

Netcatty includes 6 default rules covering common patterns.

Color: Red (#F87171)Patterns:

\[error\], \[err\]
\berror\b, \bfail(ed)?\b
\bfatal\b, \bcritical\b
\bexception\b

Matches:

ERROR: File not found
[error] Connection failed
fatal: not a git repository

Color: Yellow (#FBBF24)Patterns:

\[warn(ing)?\]
\bwarn(ing)?\b
\bcaution\b, \bdeprecated\b

Matches:

WARNING: Low disk space
[warn] Slow query detected
deprecated: use --new-flag instead

Color: Green (#34D399)Patterns:

\[ok\], \bok\b
\bsuccess(ful)?\b
\bpassed\b, \bcompleted\b
\bdone\b

Matches:

[OK] Service started
Test passed successfully
Deployment completed

Color: Blue (#3B82F6)Patterns:

\[info\], \[notice\], \[note\]
\bnotice\b, \bnote\b

Matches:

[info] Starting server...
Notice: Update available

Color: Purple (#A78BFA)Patterns:

\[debug\], \[trace\], \[verbose\]
\bdebug\b, \btrace\b, \bverbose\b

Matches:

[debug] Query took 23ms
TRACE: Function called

Color: Pink (#EC4899)Patterns:

\b(?:\d{1,3}\.){3}\d{1,3}\b (IPv4)
\b([0-9A-Fa-f]{2}[:-]){5}[0-9A-Fa-f]{2}\b (MAC)

Matches:

192.168.1.1
10.0.0.45
aa:bb:cc:dd:ee:ff

Global Configuration

Configure highlighting for all terminals.

Enabling/Disabling

keywordHighlightEnabled

boolean

default:"true"

Master toggle for keyword highlighting

UI Location:

Navigate to Settings → Terminal
Scroll to Keyword Highlighting section
Toggle Enable Keyword Highlighting

Managing Rules

UI Workflow:

Settings → Terminal → Keyword Highlighting
View list of rules with:
- Label and preview color
- Enable/disable toggle
- Pattern count
Click a rule to edit
Use + Add Rule to create new

Creating Rules

Steps:

Click + Add Rule
Configure:
- Label: Descriptive name
- Color: Click to open color picker
- Patterns: Add regex patterns (one per line)
- Enabled: Toggle on
Test against sample output
Click Save

Editing Rules

Click on existing rule
Modify:
- Label
- Color (click swatch to change)
- Patterns (add/remove/edit)
Click Update

Rule Priority

When multiple rules match the same text:

First match wins (rule order matters)
Reorder rules by dragging in the UI
More specific patterns should come before general ones

Host-Specific Highlighting

Override global rules per host.

Configuration

keywordHighlightEnabled

boolean

Enable highlighting for this host (overrides global setting)

keywordHighlightRules

KeywordHighlightRule[]

Custom rules for this host (extends or replaces global rules)

Example

{
  "hostname": "nginx-server.com",
  "username": "admin",
  "keywordHighlightEnabled": true,
  "keywordHighlightRules": [
    {
      "id": "nginx-error",
      "label": "NGINX Error",
      "patterns": [
        "\\[emerg\\]",
        "\\[alert\\]",
        "\\[crit\\]"
      ],
      "color": "#DC2626",
      "enabled": true
    },
    {
      "id": "nginx-access",
      "label": "NGINX Access Log",
      "patterns": [
        "\\b(GET|POST|PUT|DELETE|PATCH)\\b"
      ],
      "color": "#10B981",
      "enabled": true
    }
  ]
}

UI Workflow

Open Host Details panel
Navigate to Advanced → Keyword Highlighting
Click Customize Highlights
Options:
- Use Global Rules: Inherit from settings
- Extend Global Rules: Add host-specific rules
- Replace Global Rules: Use only host rules
Add/edit/remove rules
Click Save

Use Cases

Application-Specific Logs

Highlight patterns unique to an application:

NGINX/Apache log levels
Application error codes
Custom status messages

Server Type Indicators

Different colors for different server roles:

Production: Red for errors
Staging: Yellow for warnings
Development: Blue for info

Network Equipment

Highlight switch/router output:

Interface states (up/down)
VLAN IDs
MAC addresses
Protocol names (BGP, OSPF, etc.)

Writing Regex Patterns

Pattern Syntax

Patterns are JavaScript regular expressions with gi flags (global, case-insensitive). Common Patterns:

Match exact strings:

ERROR

Matches: ERROR, error, Error

Match whole words only:

\berror\b

Matches: error, Error detectedDoes NOT match: errors, errorCode

Match text in brackets:

\[error\]

Matches: [error], [ERROR](Backslashes escape the brackets)

Match variations:

\bfail(ed)?\b

Matches: fail, failed

Match multiple options:

\b(error|warning|critical)\b

Matches: error, warning, critical

Match IPv4 addresses:

\b(?:\d{1,3}\.){3}\d{1,3}\b

Matches: 192.168.1.1, 10.0.0.1

Pattern Examples

HTTP Status Codes:

\b(200|201|204|301|302|400|401|403|404|500|502|503)\b

Git Branch Names:

\b(main|master|develop|feature|hotfix)\/[\w-]+\b

Version Numbers:

\bv?\d+\.\d+\.\d+\b

Email Addresses:

\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b

File Paths:

\/[\w\/-]+\.(log|conf|cfg|txt|json|yml|yaml)

Testing Patterns

Use the Test Pattern feature in the rule editor:

Enter your pattern
Paste sample terminal output
Netcatty shows matches highlighted
Adjust pattern as needed

Test patterns on real output from your servers for best results.

Performance Considerations

Netcatty optimizes highlighting for smooth terminal operation.

Optimizations

debounceMs

number

default:"150"

Milliseconds to wait before highlighting after scroll/write

How it works:

Terminal content changes (scroll or new output)
Netcatty waits 150ms for more changes
If no changes, highlights the visible viewport
Result: Smooth scrolling with no lag

Best Practices

Pattern Efficiency

Specific patterns: \[error\] is faster than error
Anchor patterns: Use \b for word boundaries
Avoid greedy quantifiers: .* can be slow

Rule Count

Keep rules under 20 for best performance
Combine similar patterns into one rule
Disable unused rules

Alternate Buffer

Highlighting auto-disables in alternate buffer (vim, htop, etc.) to avoid impacting interactive applications.

Use Cases

System Administration

Log Monitoring:

[
  {
    "label": "Critical",
    "patterns": ["\\bcritical\\b", "\\bemerg\\b"],
    "color": "#DC2626"
  },
  {
    "label": "Service Status",
    "patterns": ["(active|running)", "(inactive|stopped|failed)"],
    "color": "#10B981"
  }
]

Development

Build Output:

[
  {
    "label": "Build Success",
    "patterns": ["Build succeeded", "Compilation complete"],
    "color": "#10B981"
  },
  {
    "label": "Build Error",
    "patterns": ["Build failed", "Compilation error"],
    "color": "#DC2626"
  }
]

Network Operations

Switch Configuration:

[
  {
    "label": "Interface Up",
    "patterns": ["link up", "connected", "administratively up"],
    "color": "#10B981"
  },
  {
    "label": "Interface Down",
    "patterns": ["link down", "disconnected", "administratively down"],
    "color": "#DC2626"
  },
  {
    "label": "MAC Address",
    "patterns": ["\\b([0-9A-Fa-f]{2}[:-]){5}[0-9A-Fa-f]{2}\\b"],
    "color": "#EC4899"
  }
]

Troubleshooting

Pattern Not Matching

Possible Causes:

Regex syntax error
Case-sensitivity (patterns are case-insensitive by default)
Need to escape special characters

Solution:

Test pattern in rule editor
Check regex syntax: regex101.com
Escape special chars: [ ] ( ) . * + ? ^ $ \ |

Highlighting Not Appearing

Possible Causes:

Highlighting disabled globally or for host
Rule is disabled
In alternate buffer (vim/htop)

Solution:

Check Settings → Terminal → Keyword Highlighting is ON
Verify rule is enabled (green toggle)
Exit vim/htop and check normal terminal

Performance Issues

Possible Causes:

Too many rules
Complex regex patterns
Very long terminal lines

Solution:

Reduce number of active rules
Simplify patterns (avoid .*)
Disable highlighting temporarily if needed

Wrong Color Appearing

Cause: Multiple rules matching, wrong prioritySolution:

Reorder rules (more specific first)
Make patterns more specific
Check for overlapping patterns

Advanced Examples

Multi-Pattern Rules

Combine multiple related patterns:

{
  "id": "kubernetes",
  "label": "Kubernetes Events",
  "patterns": [
    "\\bPodCreated\\b",
    "\\bPodStarted\\b",
    "\\bPodFailed\\b",
    "\\bPodKilled\\b",
    "\\bCrashLoopBackOff\\b",
    "\\bImagePullBackOff\\b"
  ],
  "color": "#F59E0B",
  "enabled": true
}

Contextual Highlighting

Highlight based on context:

{
  "id": "sql-queries",
  "label": "SQL Keywords",
  "patterns": [
    "\\b(SELECT|INSERT|UPDATE|DELETE|FROM|WHERE|JOIN)\\b"
  ],
  "color": "#8B5CF6",
  "enabled": true
}

Time-Based Patterns

Highlight timestamps:

{
  "id": "timestamps",
  "label": "ISO Timestamps",
  "patterns": [
    "\\d{4}-\\d{2}-\\d{2}T\\d{2}:\\d{2}:\\d{2}"
  ],
  "color": "#6366F1",
  "enabled": true
}

Custom Themes

Create terminal color schemes

Host Configuration

Apply highlighting per host

Terminal Settings

Configure terminal appearance and behavior

Get Started

Core Features

Guides

Integrations

Advanced

​Overview

​How It Works

​Highlight Rules

​Rule Structure

​Example Rule

​Default Highlight Rules

​Global Configuration

​Enabling/Disabling

​Managing Rules

​Creating Rules

​Editing Rules

​Rule Priority

​Host-Specific Highlighting

​Configuration

​Example

​UI Workflow

​Use Cases

​Writing Regex Patterns

​Pattern Syntax

​Pattern Examples

​Testing Patterns

​Performance Considerations

​Optimizations

​Best Practices

​Use Cases

​System Administration

​Development

​Network Operations

​Troubleshooting

​Advanced Examples

​Multi-Pattern Rules

​Contextual Highlighting

​Time-Based Patterns

​Related Resources

Custom Themes

Host Configuration

Terminal Settings

Overview

How It Works

Highlight Rules

Rule Structure

Example Rule

Default Highlight Rules

Global Configuration

Enabling/Disabling

Managing Rules

Creating Rules

Editing Rules

Rule Priority

Host-Specific Highlighting

Configuration

Example

UI Workflow

Use Cases

Writing Regex Patterns

Pattern Syntax

Pattern Examples

Testing Patterns

Performance Considerations

Optimizations

Best Practices

Use Cases

System Administration

Development

Network Operations

Troubleshooting

Advanced Examples

Multi-Pattern Rules

Contextual Highlighting

Time-Based Patterns

Related Resources