Compression

Compression

Concept of the skill

Data and context compression — SaaS payload optimization (Zstd, Brotli, Gzip), database storage compression, and AI context-window compression (semantic summarization, token pruning) — applied to cut API latency, storage cost, and long-running agent context pressure.

Domain Context

What is this skill? This skill provides expertise in data and context compression: SaaS payload optimization (Zstd, Brotli, Gzip), database storage compression, and AI context window compression (Semantic Summarization, Token Pruning). Use when optimizing API latency, reducing storage costs, or managing long-running agent sessions near context limits. Do NOT use for image/video lossy compression (use product-photo) or file archiving.

Grounding Sources

Use primary codec and platform references for factual claims: RFC 8878 for Zstandard, RFC 7932 for Brotli, RFC 1952 for Gzip, MDN and HTTP docs for Accept-Encoding / Content-Encoding, and PostgreSQL's TOAST and default_toast_compression documentation for database storage behavior. Keep agent context-compression guidance separate from HTTP/database codec facts: summaries are correct only when they preserve intent, outcome, and evidence paths.

Coverage

SaaS payload compression (Zstd, Brotli, Gzip algorithm selection, level tuning, content negotiation), PostgreSQL storage compression (TOAST with pglz/lz4 where supported, plus deliberate application-layer blob compression), and AI context window compression (semantic summarization, token pruning, dead context identification, state re-injection). Covers the decision tree for matching algorithms to data types, the Accept-Encoding negotiation order, and the three-phase token pruning workflow.

Philosophy of the skill

Compression is the science of increasing information density. In a modern SaaS, it applies at two layers: the Infrastructure Layer (reducing bytes on the wire/disk) and the Intelligence Layer (reducing tokens in the context window). Without this skill, agents default to generic compression advice that ignores the specific algorithm-to-data-type mapping (e.g., using Gzip everywhere instead of Zstd for dynamic API payloads) and fail to recognize that sub-1KB payloads should skip compression entirely. On the intelligence side, agents routinely let context windows bloat with dead research turns instead of applying structured summarization that preserves evidence paths.

1. SaaS Data Compression Decision Tree

Match the compression algorithm to the data type and lifecycle.

Implementation Rules

• Negotiation: Always check Accept-Encoding header. Order: zstd > br > gzip.
• Level Selection: Use Level 3 for dynamic runtime; Level 11 for static build-time.
• Header Safety: Ensure Vary: Accept-Encoding is set to prevent cache pollution.

2. AI Context Compression

Protect the context window by maximizing token density.

Semantic Summarization

• Pattern: Replace raw logs/code with high-density Markdown summaries.
• Rule: A summary must preserve Intent, Outcome, and Evidence Paths while removing boilerplate.

Token Pruning (The "Surgical Cut")

• Phase 1: Identify "Dead Context" (e.g., redundant file reads, failed research turns).
• Phase 2: Use /clear or /compact to drop the bottom 50% of the session history.
• Phase 3: Re-inject the "State of the Union" summary via Memory MCP.

Source: skills/token-efficiency/SKILL.md (Adjacent)

3. Storage Compression (Postgres)

Optimize for cost and performance at the database layer.

• TOAST Compression: PostgreSQL TOAST can compress large values with pglz by default and lz4 when PostgreSQL is built with lz4 support. Do not claim native TOAST Zstd unless the deployed database explicitly provides it.
• Blob Compression: For extremely large blobs (>10MB), compress in the application layer (Node.js zstd bindings) before storing as BYTEA.

4. Verification Checklist

COMPRESSION CHECK
=================
[ ] Static assets pre-compressed with Brotli (Level 11)
[ ] API middleware supports Zstd with Gzip fallback
[ ] Vary: Accept-Encoding header present
[ ] AI context summary preserves Evidence Paths
[ ] redundant research/file reads pruned from session
[ ] DB compression matches the deployed database's actual TOAST options (`pglz` / `lz4`) or a deliberate application-layer codec
[ ] Payloads < 1KB skip compression to avoid overhead

Verification

After applying this skill, verify:

• Algorithm matches data type per the decision tree (static=Brotli, dynamic API=Zstd when supported, DB=TOAST pglz/lz4 or explicit application-layer codec)
• Accept-Encoding negotiation respects the zstd > br > gzip priority order
• Vary: Accept-Encoding header is set to prevent cache pollution
• Small payloads (<1KB) are not compressed (overhead exceeds savings)
• Context summaries preserve Intent, Outcome, and Evidence Paths
• Token pruning removes dead context (failed research turns, redundant reads) before injecting fresh state

Do NOT Use When

Skill Graph context

Classification

• Subject: backend-engineering
• Public: true
• Domain: engineering/data
• Scope: Data and context compression — SaaS payload optimization (Zstd, Brotli, Gzip), database storage compression, and AI context-window compression (semantic summarization, token pruning) — applied to cut API latency, storage cost, and long-running agent context pressure. Portable across any service or agent runtime; principle-grounded, not repo-bound. Excludes lossy image/video compression (product-photo) and file archiving.

When to use

• Triggers: compression-skill, context-compression, payload-optimization

Related skills

• Related: context-window, context-management, summarization, cognitive-load-theory

Grounding

• Mode: universal
• Truth sources: https://www.rfc-editor.org/info/rfc8878, https://datatracker.ietf.org/doc/html/rfc7932, https://www.rfc-editor.org/rfc/rfc1952, https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Accept-Encoding, https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/Content-Encoding, https://www.postgresql.org/docs/current/storage-toast.html, https://www.postgresql.org/docs/current/runtime-config-client.html#GUC-DEFAULT-TOAST-COMPRESSION

Keywords

• compression, Zstd, Brotli, Gzip, context window, token efficiency, semantic summarization, payload reduction, DB TOAST