RX Data Store

Skill by ara.so — Daily 2026 Skills collection.

RX is an embedded data store for JSON-shaped data. Encode once, then query the encoded document in place — no parsing, no object graph, no GC pressure. Think of it as no-SQL SQLite: unstructured data with database-style random access.

Key benefits:

• O(1) array access, O(log n) object key lookup on encoded data
• Automatic deduplication of values and shared schemas
• Text-safe encoding (copy-paste friendly, no binary tooling needed)
• Minimal heap allocations (~10 vs millions for JSON parsing)
• ~18x compression on real deployment manifests (92 MB → 5.1 MB)

Installation

npm install @creationix/rx        # library
npm install -g @creationix/rx     # CLI (global)
npx @creationix/rx data.rx        # CLI (one-off)

Core API

String API (most common)

import { stringify, parse } from "@creationix/rx";

// Encode
const rx = stringify({ users: ["alice", "bob"], version: 3 });
// Returns a string — store it anywhere you'd store JSON text

// Decode (returns a read-only Proxy)
const data = parse(rx) as any;
data.users[0]         // "alice"
data.version          // 3
Object.keys(data)     // ["users", "version"]
JSON.stringify(data)  // works — full JS interop

Uint8Array API (performance-critical paths)

import { encode, open } from "@creationix/rx";

const buf = encode({ path: "/api/users", status: 200 });
const data = open(buf) as any;
data.path    // "/api/users"
data.status  // 200

Inspect API (lazy AST)

import { encode, inspect } from "@creationix/rx";

const buf = encode({ name: "alice", scores: [10, 20, 30] });
const root = inspect(buf);

root.tag          // ":"
root[0].tag       // "," (a string key)
root[0].value     // "name"
root.length       // 4 (key, value, key, value)

// Iterate children
for (const child of root) {
  console.log(child.tag, child.b64);
}

// Object helpers
for (const [key, val] of root.entries()) { /* ... */ }
const node = root.index("name");   // key lookup → node
const elem = root.index(2);        // array index → node

// Filtered key search (O(log n + m) on indexed objects)
for (const [key, val] of root.filteredKeys("/api/")) { /* ... */ }

Escape hatch to underlying buffer

import { handle } from "@creationix/rx";

const h = handle(data.nested);
// h.data: Uint8Array
// h.right: byte offset

Encoding Options

stringify(data, {
  // Add sorted indexes to containers with >= N entries (enables O(log n) lookup)
  // Use 0 for all containers, false to disable entirely
  indexes: 10,

  // External refs — shared dictionary of known values for cross-document dedup
  refs: { R: ["/api/users", "/api/teams"] },

  // Streaming — receive chunks as they're produced
  onChunk: (chunk: string, offset: number) => process.stdout.write(chunk),
});

encode(data, {
  indexes: 10,
  refs: { R: ["/api/users", "/api/teams"] },
  onChunk: (chunk: Uint8Array, offset: number) => { /* ... */ },
});

If the encoder used external refs, pass the same dictionary to the decoder:

const data = parse(payload, { refs: { R: ["/api/users", "/api/teams"] } });
const data = open(buf, { refs: { R: ["/api/users", "/api/teams"] } });

CLI

rx data.rx                         # pretty-print as tree (default on TTY)
rx data.rx -j                      # convert to JSON
rx data.json -r                    # convert to RX
cat data.rx | rx                   # read from stdin (auto-detect format)
rx data.rx -s key 0 sub            # select a sub-value: data["key"][0]["sub"]
rx data.rx -o out.json             # write to file
rx data.rx --ast                   # output encoding structure as JSON
rx data.rx -w                      # write converted file (.json↔.rx)

Full CLI flags:

Shell completions:

rx --completions setup zsh   # or bash

Tip — paged, colorized viewing:

p() { rx "$1" -t -c | less -RFX; }

Proxy Behavior

The value returned by parse/open is read-only:

obj.newKey = 1;      // throws TypeError
delete obj.key;      // throws TypeError
"key" in obj;        // works (zero-alloc key search)
obj.nested === obj.nested  // true (container Proxies are memoized)

Supported operations on the Proxy:

• Property access: data.key, data[0]
• Object.keys(), Object.entries(), Object.values()
• for...of, for...in
• Array.isArray()
• .map(), .filter(), .find(), .reduce()
• Spread and destructuring
• JSON.stringify()

Common Patterns

Build-step: convert JSON artifact to RX

import { readFileSync, writeFileSync } from "fs";
import { stringify } from "@creationix/rx";

const json = JSON.parse(readFileSync("manifest.json", "utf-8"));
const rx = stringify(json, { indexes: 10 });
writeFileSync("manifest.rx", rx, "utf-8");

Runtime: sparse read from large RX file

import { readFileSync } from "fs";
import { parse } from "@creationix/rx";

const manifest = parse(readFileSync("manifest.rx", "utf-8")) as any;

// Only the accessed values are decoded — everything else is skipped
const route = manifest.routes["/dashboard/projects"];
console.log(route.title, route.component, route.auth);

Streaming encode to stdout

import { stringify } from "@creationix/rx";

stringify(largeData, {
  onChunk: (chunk, offset) => process.stdout.write(chunk),
});

Using external refs for cross-document deduplication

import { stringify, parse } from "@creationix/rx";

const sharedRefs = { R: ["/api/users", "/api/teams", "/api/projects"] };

// Encode multiple documents sharing the same ref dictionary
const doc1 = stringify(data1, { refs: sharedRefs });
const doc2 = stringify(data2, { refs: sharedRefs });

// Decode with the same dictionary
const val1 = parse(doc1, { refs: sharedRefs }) as any;
const val2 = parse(doc2, { refs: sharedRefs }) as any;

Low-level inspect traversal (zero allocation)

import { encode, inspect } from "@creationix/rx";

const buf = encode(routes);
const root = inspect(buf);

// Walk object entries without creating JS objects
if (root.tag === ":") {
  for (const [key, val] of root.entries()) {
    if (key.value === "/dashboard") {
      console.log("Found:", val.index("title").value);
      break;
    }
  }
}

Type-safe usage pattern

import { parse } from "@creationix/rx";

interface Route {
  title: string;
  component: string;
  auth: boolean;
}

interface Manifest {
  routes: Record<string, Route>;
  version: number;
}

// Cast after parse — RX Proxy supports all read operations
const manifest = parse(rxString) as unknown as Manifest;
const dashboard = manifest.routes["/dashboard"];

Format Reference

RX is a text encoding — not human-readable like JSON, but safe to copy-paste.

Every value is read right-to-left. The parser scans left past base64 digits to find a tag character:

[body][tag][b64 varint]
            ◄── read this way ──

Tags: + integer · * decimal · , string · ' ref/literal · : object · ; array · ^ pointer · . chain · # index

When to Use RX vs Alternatives

Troubleshooting

TypeError: Cannot set property on decoded value The Proxy returned by parse/open is read-only by design. To mutate, spread into a plain object first:

const mutable = { ...parse(rx) };
mutable.newKey = "value"; // works

Decoded value looks correct but instanceof Array fails Use Array.isArray(val) instead — this is correctly intercepted by the Proxy.

External refs mismatch / wrong values decoded Ensure the exact same refs dictionary (same keys, same arrays, same order) is passed to both stringify/encode and parse/open.

CLI not found after global install

npm install -g @creationix/rx
# If still not found, check your npm global bin path:
npm bin -g

Inspecting encoded bytes

rx data.rx --ast    # shows encoding structure with tags and offsets

Or use the live viewer at rx.run — paste RX or JSON directly.

Performance: lookups slower than expected Ensure indexes threshold is set appropriately when encoding. For large objects (e.g., 35k keys), use indexes: 0 to index all containers:

stringify(data, { indexes: 0 });

Resources

• rx.run — live web viewer, paste RX or JSON to inspect
• docs/rx-format.md — full format spec with grammar and railroad diagrams
• docs/cursor-api.md — low-level zero-allocation cursor API
• samples/ — example datasets (route manifest, RPG state, emoji metadata, sensor telemetry)