OmniRoute/docs/compression/COMPRESSION_RULES_FORMAT.md

title	version	lastUpdated
Compression Rules Format	3.8.1	2026-05-13

Compression Rules Format

Compression rules are JSON files loaded at runtime. They are intentionally data-only so new language packs and RTK command filters can be reviewed without changing engine code.

Canonical schema (source of truth): open-sse/services/compression/rules/_schema.json (JSON Schema draft 2020-12). The examples below are illustrative — when in doubt, validate your pack against _schema.json.

Caveman Rule Packs

Caveman rule packs live under:

open-sse/services/compression/rules/<language>/<pack>.json

Each pack contains replacements that apply to normal prose after protected regions are isolated.

{
  "language": "en",
  "category": "filler",
  "rules": [
    {
      "name": "question_to_directive",
      "pattern": "\\b(?:Can you explain why|Could you show me how)\\b\\s*",
      "replacement": "Explain why ",
      "replacementMap": {
        "can you explain why": "Explain why ",
        "could you show me how": "Show how "
      },
      "flags": "gi",
      "context": "all",
      "category": "context",
      "minIntensity": "lite",
      "description": "Convert verbose questions into direct requests."
    }
  ]
}

Caveman Fields

Field	Required	Description
language	yes	BCP-47-like language key such as en, pt-BR, es
category	yes	Pack category filename/category, for example filler or dedup
rules	yes	Array of regex replacement rules
rules[].name	yes	Stable rule name
rules[].pattern	yes	JavaScript regex source
rules[].flags	no	JavaScript regex flags; default gi
rules[].replacement	no	Replacement string or fallback when replacementMap misses
rules[].replacementMap	no	Match-specific replacements keyed by normalized matched text
rules[].context	no	all, user, assistant, or system; default all
rules[].category	no	filler, context, structural, dedup, terse, or ultra
rules[].minIntensity	no	lite, full, or ultra; default lite
rules[].description	no	Human-readable rule summary

Use flags when case-sensitive matching matters, for example article removal before lowercase prose without stripping the OpenAI API. Use replacementMap when one regex has multiple alternatives that need different outputs; this keeps JSON rule packs data-only while preserving the behavior of the richer built-in TypeScript replacement functions.

RTK Filter Packs

RTK filters live under:

open-sse/services/compression/engines/rtk/filters/<filter>.json

Each filter describes how to recognize and compress a command-output family.

{
  "id": "test-vitest",
  "label": "Vitest output",
  "category": "test",
  "priority": 92,
  "match": {
    "outputTypes": ["test-vitest"],
    "commands": ["vitest", "npm test", "npm run test"],
    "patterns": ["\\bFAIL\\b", "\\bPASS\\b", "\\bTest Files\\b"]
  },
  "rules": {
    "stripAnsi": true,
    "replace": [{ "pattern": "\\s+\\[[0-9]+ms\\]", "replacement": "" }],
    "matchOutput": [
      { "pattern": "All tests passed", "message": "vitest: ok", "unless": "FAIL|Error:" }
    ],
    "includePatterns": ["FAIL", "Error:", "Test Files", "Tests"],
    "dropPatterns": ["^\\s*$", "Duration\\s+\\d+"],
    "collapsePatterns": ["^\\s+at "],
    "deduplicate": true,
    "truncateLineAt": 240,
    "maxLines": 160,
    "headLines": 24,
    "tailLines": 40,
    "onEmpty": "vitest: ok",
    "filterStderr": false
  },
  "preserve": {
    "errorPatterns": ["FAIL", "Error:", "AssertionError"],
    "summaryPatterns": ["Test Files", "Tests", "Snapshots"]
  },
  "tests": [
    {
      "name": "keeps failing tests",
      "command": "vitest",
      "input": "FAIL test/a.test.ts\\nError: boom\\nTest Files 1 failed",
      "expected": "FAIL test/a.test.ts\\nError: boom\\nTest Files 1 failed"
    }
  ]
}

RTK Fields

Field	Required	Description
id	yes	Stable filter id
label	yes	Dashboard-readable name
category	yes	Filter family: git, test, build, shell, docker, package, infra, cloud, generic
priority	no	Higher priority wins when multiple filters match
match.outputTypes	no	Detector output ids that select this filter
match.commands	no	Command tokens that select this filter
match.patterns	no	Regex patterns that select this filter from output text
rules.stripAnsi	no	Remove ANSI escape sequences before regex stages
rules.replace	no	Ordered regex substitutions applied line by line
rules.matchOutput	no	Short-circuit output rules with optional unless guard
rules.includePatterns	no	Lines to prefer preserving
rules.dropPatterns	no	Lines to remove as noise
rules.collapsePatterns	no	Repeated matching lines that can be collapsed
rules.deduplicate	no	Collapse duplicate normalized lines
rules.truncateLineAt	no	Unicode-safe per-line character limit
rules.maxLines	no	Maximum retained lines before tail preservation
rules.headLines	no	Head lines retained during truncation
rules.tailLines	no	Tail lines retained for recent context
rules.onEmpty	no	Fallback message when filtering removes all content
rules.filterStderr	no	Normalize common stderr prefixes before later filtering stages
preserve.errorPatterns	no	Error lines that should survive truncation
preserve.summaryPatterns	no	Summary lines that should survive truncation
tests[]	no	Inline verification samples used by the RTK verify gate

RTK applies declarative stages in this order: stripAnsi, filterStderr, replace, matchOutput, dropPatterns/includePatterns, truncateLineAt, headLines/tailLines, maxLines, and onEmpty.

Custom filters can be loaded from:

1. Project .rtk/filters.json files only after a matching .rtk/trust.json hash is present or trustProjectFilters is enabled.
2. Global DATA_DIR/rtk/filters.json.
3. Built-in filters.

Project/global custom files may contain one filter object or an array of filter objects. Invalid custom filters are skipped with diagnostics; invalid built-in filters fail validation.

Project trust file:

{
  "filtersSha256": "0123456789abcdef..."
}

The environment override OMNIROUTE_RTK_TRUST_PROJECT_FILTERS=1 trusts project filters without a hash and should be limited to controlled local development.

Safety Rules

• Keep rules idempotent: running the same filter twice should not corrupt output.
• Preserve exact error text, file paths, line numbers, and command summaries where possible.
• Avoid rules that modify code blocks, JSON payloads, URLs, or secrets.
• Add unit coverage for new command families in detector/filter tests.
• Add tests[] samples to every built-in filter and to shared custom filters.

Validation

Rule packs are validated before use. Built-in Caveman packs and built-in RTK filters fail fast during validation so broken release assets are caught before shipment. Custom RTK filters are skipped with diagnostics when parsing or trust validation fails.

Focused validation:

node --import tsx/esm --test tests/unit/compression/rule-loader.test.ts tests/unit/compression/language-packs.test.ts
node --import tsx/esm --test tests/unit/compression/rtk-verify.test.ts tests/unit/compression/rtk-dsl-pipeline.test.ts