Development

Hotline Protocol

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Core Documentation

• Documentation Home
• Glossary / Terms
• Protocol History

Technical Specifications

• Transaction IDs
• Field Definitions
• Access Bits
• Error Codes

Binary & Data

• FILP/RFLT Specs
• News Headers
• Logic Sequences

External Networking

• Tracker (HTRK)
• HTTP Tunneling
• Global Server

Assets

• Icon Gallery
• Community Icons

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Ecosystem & Derivative Protocols

While the Hotline 1.9 Standard is the primary focus of this wiki, several related projects and "forked" protocols exist. Understanding these is essential for cross-client compatibility.

Official & Extended Hotline Specs

These resources cover the official Hotsprings releases and the community-driven extensions that kept the protocol alive.

• Hotsprings Protocol – The finalized Hotline 1.9.x specification.
• Hotline 1.5 Specification – The legacy foundation used by older clients.
• DateParameters – Technical breakdown of how Hotline handles 68k-era timestamps.
• Unofficial_Protocol_Extensions – Specs for HOPE and other modern community enhancements.

Branch Protocols (Non-Compatible)

During the "Hotline Wars" of the early 2000s, several developers built alternative systems. While they share "Hotline DNA," they are generally not protocol-compatible with standard Hotline servers.

Haxial KDX

KDX was a major successor that added encryption and a more modern UI, though it moved away from the open Hotline standard.

• KDX_Protocol – The encrypted successor specification.

Carracho

A Mac-centric alternative that gained massive popularity for its refined UI and improved stability over the original 1.5 codebase.

• Carracho protocol – Detailed spec for Carracho-specific transactions.

Abandoned & Historical Projects

• AppWarrior – Information on the early alternative Hotline client development.