TypeScript

Agent-First Data (AFDATA) — Suffix-driven output formatting and protocol templates for AI agents.

The field name is the schema. Agents read latency_ms and know milliseconds, api_key_secret and know to redact, no external schema needed.

Installation

npm install agent-first-data

Quick Example

A backup tool invoked from the CLI — flags, env vars, and config all use the same suffixes:

API_KEY_SECRET=sk-1234 cloudback --timeout-s 30 --max-file-size-bytes 10737418240 /data/backup.tar.gz

For CLI diagnostics, enable log categories explicitly:

--log startup,request,progress,retry,redirect
--verbose   # shorthand for all categories

Without these flags, startup diagnostics should stay off by default.

The tool reads env vars, flags, and config — all with AFDATA suffixes — and can emit a startup diagnostic event:

import { buildJson, outputJson, outputYaml, outputPlain } from "agent-first-data";

const startup = buildJson(
  "log",
  {
    event: "startup",
    config: { timeout_s: 30, max_file_size_bytes: 10737418240 },
    args: { input_path: "/data/backup.tar.gz" },
    env: { API_KEY_SECRET: process.env.API_KEY_SECRET ?? null },
  },
);

Three output formats, same data:

JSON:  {"code":"log","event":"startup","args":{"input_path":"/data/backup.tar.gz"},"config":{"max_file_size_bytes":10737418240,"timeout_s":30},"env":{"API_KEY_SECRET":"***"}}
YAML:  code: "log"
       event: "startup"
       args:
         input_path: "/data/backup.tar.gz"
       config:
         max_file_size: "10.0GB"
         timeout: "30s"
       env:
         API_KEY: "***"
Plain: args.input_path=/data/backup.tar.gz code=log event=startup config.max_file_size=10.0GB config.timeout=30s env.API_KEY=***

--timeout-s → timeout_s → timeout: 30s. API_KEY_SECRET → API_KEY: "***". The suffix is the schema.

API Reference

Total: 15 public APIs and 2 types + AFDATA logging (3 protocol builders + 2 redacted value helpers + 4 output functions + 1 internal + 1 utility + 4 CLI helpers + OutputFormat + RedactionPolicy)

Protocol Builders (returns JsonValue)

Build AFDATA protocol structures. Return JSON-serializable objects for transport payloads.

type JsonValue = string | number | boolean | null | JsonValue[] | { [key: string]: JsonValue };

// Success (result)
buildJsonOk(result: JsonValue, trace?: JsonValue): JsonValue

// Error (simple message, optional hint)
buildJsonError(message: string, hint?: string, trace?: JsonValue): JsonValue

// Generic (any code + fields)
buildJson(code: string, fields: JsonValue, trace?: JsonValue): JsonValue

Redacted Values (returns JsonValue)

Use these before raw HTTP/MCP/SSE serializers that do not call outputJson.

redactedValue(value: unknown): JsonValue
redactedValueWith(value: unknown, redactionPolicy: RedactionPolicy): JsonValue

Use case: structured protocol payloads (frameworks automatically serialize)

Example:

import { buildJsonOk, buildJsonError, buildJson } from "agent-first-data";

// Startup
const startup = buildJson(
  "log",
  {
    event: "startup",
    config: { api_key_secret: "sk-123", timeout_s: 30 },
    args: { config_path: "config.yml" },
    env: { RUST_LOG: "info" },
  },
);

// Success (always include trace)
const response = buildJsonOk(
  { user_id: 123 },
  { duration_ms: 150, source: "db" },
);

// Error
const error = buildJsonError("user not found", undefined, { duration_ms: 5 });

// Error with hint
const errorHint = buildJsonError("wallet not found", "list wallets with: afpay wallet list", { duration_ms: 5 });

// Specific error code
const notFound = buildJson(
  "not_found",
  { resource: "user", id: 123 },
  { duration_ms: 8 },
);

CLI/Log Output (returns string)

Format values for CLI output and logs. outputJson uses full _secret redaction by default. outputJsonWith supports explicit scoped policies. YAML and Plain always redact _secret and apply human-readable formatting.

outputJson(value: JsonValue): string   // Single-line JSON, original keys, for programs/logs
outputJsonWith(value: JsonValue, redactionPolicy: RedactionPolicy): string
outputYaml(value: JsonValue): string   // Multi-line YAML, keys stripped, values formatted
outputPlain(value: JsonValue): string  // Single-line logfmt, keys stripped, values formatted

enum RedactionPolicy {
  RedactionTraceOnly = "RedactionTraceOnly",
  RedactionNone = "RedactionNone",
  RedactionStrict = "RedactionStrict",
}

Example:

import { outputJson, outputYaml, outputPlain } from "agent-first-data";

const data = {
  user_id: 123,
  api_key_secret: "sk-1234567890abcdef",
  created_at_epoch_ms: 1738886400000,
  file_size_bytes: 5242880,
};

// JSON (secrets redacted, original keys, raw values)
console.log(outputJson(data));
// {"api_key_secret":"***","created_at_epoch_ms":1738886400000,"file_size_bytes":5242880,"user_id":123}

// YAML (keys stripped, values formatted, secrets redacted)
console.log(outputYaml(data));
// ---
// api_key: "***"
// created_at: "2025-02-07T00:00:00.000Z"
// file_size: "5.0MB"
// user_id: 123

// Plain logfmt (keys stripped, values formatted, secrets redacted)
console.log(outputPlain(data));
// api_key=*** created_at=2025-02-07T00:00:00.000Z file_size=5.0MB user_id=123

Internal Tools

internalRedactSecrets(value: JsonValue): void  // Manually redact secrets in-place

Most users don’t need this. Output functions automatically protect secrets.

Utility Functions

parseSize(s: string): number | null  // Parse "10M" → bytes

Returns null for invalid, negative, overflow, or non-safe-integer values.

Example:

import { parseSize } from "agent-first-data";

parseSize("10M");  // 10485760
parseSize("1.5K"); // 1536
parseSize("512");  // 512

CLI Helpers (for tools built on AFDATA)

Shared helpers that prevent flag-parsing drift between CLI tools. Use these instead of reimplementing --output and --log handling in each tool.

type OutputFormat = "json" | "yaml" | "plain"

cliParseOutput(s: string): OutputFormat             // Parse --output flag; throws on unknown
cliParseLogFilters(entries: string[]): string[]     // Normalize --log: trim, lowercase, dedup, remove empty
cliOutput(value: JsonValue, format: OutputFormat): string  // Dispatch to outputJson/Yaml/Plain
buildCliError(message: string, hint?: string): JsonValue  // {code:"error", error_code:"invalid_request", hint?, retryable:false, trace:{duration_ms:0}}

Canonical pattern — parse all flags before doing work, emit JSONL errors to stdout:

import {
  type OutputFormat, cliParseOutput, cliParseLogFilters,
  cliOutput, buildCliError, outputJson,
} from "agent-first-data";

let fmt: OutputFormat;
try {
  fmt = cliParseOutput(outputArg);
} catch (e) {
  console.log(outputJson(buildCliError((e as Error).message)));
  process.exit(2);
}

const log = cliParseLogFilters(logArg ? logArg.split(",") : []);
// ... do work ...
console.log(cliOutput(result, fmt));

See examples/agent_cli.ts for the complete working example (npx tsx --test examples/agent_cli.ts).

Usage Examples

Example 1: REST API

import { buildJsonOk } from "agent-first-data";
import express from "express";

const app = express();

app.get("/users/:id", (req, res) => {
  const response = buildJsonOk(
    { user_id: Number(req.params.id), name: "alice" },
    { duration_ms: 150, source: "db" },
  );
  // API returns raw JSON — no output processing, no key stripping
  res.json(response);
});

Example 2: CLI Tool (Complete Lifecycle)

import { buildJsonOk, buildJson, outputYaml, outputPlain } from "agent-first-data";

// 1. Startup
const startup = buildJson(
  "log",
  {
    event: "startup",
    config: { api_key_secret: "sk-sensitive-key", timeout_s: 30 },
    args: { input_path: "data.json" },
    env: { RUST_LOG: "info" },
  },
);
console.log(outputYaml(startup));
// ---
// code: "log"
// event: "startup"
// args:
//   input_path: "data.json"
// config:
//   api_key: "***"
//   timeout: "30s"
// env:
//   RUST_LOG: "info"

// 2. Progress
const progress = buildJson(
  "progress",
  { current: 3, total: 10, message: "processing" },
  { duration_ms: 1500 },
);
console.log(outputPlain(progress));
// code=progress current=3 message=processing total=10 trace.duration=1.5s

// 3. Result
const result = buildJsonOk(
  {
    records_processed: 10,
    file_size_bytes: 5242880,
    created_at_epoch_ms: 1738886400000,
  },
  { duration_ms: 3500, source: "file" },
);
console.log(outputYaml(result));
// ---
// code: "ok"
// result:
//   created_at: "2025-02-07T00:00:00.000Z"
//   file_size: "5.0MB"
//   records_processed: 10
// trace:
//   duration: "3.5s"
//   source: "file"

Example 3: JSONL Output

import { buildJsonOk, outputJson } from "agent-first-data";

const result = buildJsonOk(
  { status: "success" },
  { duration_ms: 250, api_key_secret: "sk-123" },
);

// Print JSONL to stdout (secrets redacted, one JSON object per line)
// Channel policy: machine-readable protocol/log events must not use stderr.
console.log(outputJson(result));
// {"code":"ok","result":{"status":"success"},"trace":{"api_key_secret":"***","duration_ms":250}}

Complete Suffix Example

import { outputYaml, outputPlain } from "agent-first-data";

const data = {
  created_at_epoch_ms: 1738886400000,
  request_timeout_ms: 5000,
  cache_ttl_s: 3600,
  file_size_bytes: 5242880,
  payment_msats: 50000000,
  price_usd_cents: 9999,
  success_rate_percent: 95.5,
  api_key_secret: "sk-1234567890abcdef",
  user_name: "alice",
  count: 42,
};

// YAML output (keys stripped, values formatted, secrets redacted)
console.log(outputYaml(data));
// ---
// api_key: "***"
// cache_ttl: "3600s"
// count: 42
// created_at: "2025-02-07T00:00:00.000Z"
// file_size: "5.0MB"
// payment: "50000000msats"
// price: "$99.99"
// request_timeout: "5.0s"
// success_rate: "95.5%"
// user_name: "alice"

// Plain logfmt output (same transformations, single line)
console.log(outputPlain(data));
// api_key=*** cache_ttl=3600s count=42 created_at=2025-02-07T00:00:00.000Z file_size=5.0MB payment=50000000msats price=$99.99 request_timeout=5.0s success_rate=95.5% user_name=alice

AFDATA Logging

AFDATA-compliant structured logging. Every log line is formatted using the library’s own outputJson/outputPlain/outputYaml functions. Span fields are carried via AsyncLocalStorage (async-safe), automatically flattened into each log line. Zero dependencies beyond Node.js built-ins.

API

import { log, span, initJson, initPlain, initYaml } from "agent-first-data";

// Format selectors — set the output format for all subsequent log calls
initJson()    // Single-line JSONL (secrets redacted, original keys) — default
initPlain()   // Single-line logfmt (keys stripped, values formatted)
initYaml()    // Multi-line YAML (keys stripped, values formatted)

// Logger — each method outputs a single log line to stdout
log.trace(msg, fields?)
log.debug(msg, fields?)
log.info(msg, fields?)
log.warn(msg, fields?)
log.error(msg, fields?)

// Span — run fn with additional fields on all log events
span<T>(fields, fn: () => T): T  // works with sync and async functions

Setup

import { log, initJson, initPlain, initYaml } from "agent-first-data";

// JSON output for production (one JSONL line per event, secrets redacted)
initJson();  // default, can be omitted

// Plain logfmt for development (keys stripped, values formatted)
initPlain();

// YAML for detailed inspection (multi-line, keys stripped, values formatted)
initYaml();

Log Output

Output format depends on the init function used.

log.info("Server started");
// JSON:  {"timestamp_epoch_ms":1739000000000,"message":"Server started","code":"info"}
// Plain: code=info message="Server started" timestamp_epoch_ms=1739000000000
// YAML:  ---
//        code: "info"
//        message: "Server started"
//        timestamp_epoch_ms: 1739000000000

log.warn("DNS lookup failed", { error: "timeout", domain: "example.com" });
// JSON:  {"timestamp_epoch_ms":...,"message":"DNS lookup failed","error":"timeout","domain":"example.com","code":"warn"}
// Plain: code=warn domain=example.com error=timeout message="DNS lookup failed" ...

Span Support

Use span() to add fields to all log events within the callback. Spans nest and work with both sync and async functions.

import { log, span } from "agent-first-data";

await span({ request_id: "abc-123" }, async () => {
  log.info("Processing");
  // {"timestamp_epoch_ms":...,"message":"Processing","request_id":"abc-123","code":"info"}

  await span({ step: "validate" }, async () => {
    log.info("Validating input");
    // {"timestamp_epoch_ms":...,"message":"Validating input","request_id":"abc-123","step":"validate","code":"info"}
  });
});

Custom Code Override

The code field defaults to the log level. Override with an explicit field:

log.info("Server ready", { code: "log", event: "startup" });
// {"timestamp_epoch_ms":...,"message":"Server ready","code":"log","event":"startup"}

Output Fields

Every log line contains:

Log Output Formats

All three formats use the library’s own output functions, so AFDATA suffix processing applies to log fields too:

All formats automatically redact _secret fields in log output.

Output Formats

Three output formats for different use cases:

All formats automatically redact _secret fields.

Supported Suffixes

• Duration: _ms, _s, _ns, _us, _minutes, _hours, _days
• Timestamps: _epoch_ms, _epoch_s, _epoch_ns, _rfc3339
• Size: _bytes (auto-scales to KB/MB/GB/TB), _size (config input, pass through)
• Currency: _msats, _sats, _btc, _usd_cents, _eur_cents, _jpy, _{code}_cents
• Other: _percent, _secret (auto-redacted in all formats)

TypeScript uses JavaScript number for JSON values, so _epoch_ns values above Number.MAX_SAFE_INTEGER lose precision. Prefer _epoch_ms for JSON interchange, or convert nanosecond values before formatting.

Repository

This package is part of the agent-first-data repository, which also contains:

• spec/ — Full AFDATA specification with suffix definitions, protocol format rules, and cross-language test fixtures
• skills/ — AI coding agent skill for working with AFDATA conventions

To run tests, clone the full repository (tests use shared cross-language fixtures from spec/fixtures/):

git clone https://github.com/agentfirstkit/agent-first-data
cd agent-first-data/typescript
npm test

License

MIT