Install

NPM

npm install @nirelc/microconf

Bun

bun install @nirelc/microconf

Usage

import { defineConfig, t, env } from "@nirelc/microconf";

const config = defineConfig({
  schema: {
    port: t.number().min(0).max(65535).default(8080),
  },
  // optional. With no sources (or sources: []), use schema defaults only
  sources: [env()],
});

Sources

For each field, sources are checked in array order:

• missing value allows the next source to run
• invalid value cause ParseConfigError, other sources and defaults can't replace it
• if every source is missing the value, the schema is parsed with undefined and .default() or .optional() are applied

Sources return undefined from load(meta) only for missing values. For existing values, return the schema's ParseResult, including validation failures. A successful result containing data: undefined is still a resolved value, not a missing one.

Available sources:

defaults()

defaults() loads from schema .default() values

Defaults are always applied last by defineConfig, including with sources: []. You don't need to add defaults() explicitly

env()

env() loads from env variables. We doesn't load .env files!

Schema keys are converted to env variable names by:

• add prefix if provided. e.g., with prefix APP_, token becomes APP_TOKEN
• camelCase -> camel_Case
• all chars -> UPPERCASE
• nested keys are converted to flat env variable names by delimiter (default: __)

e.g.:

// index.ts
const config = defineConfig({
  schema: {
    nested: {
      key: t.string(),
    },
  },
  sources: [env()],
});

// .env
NESTED__KEY = hello;

this source can be configured with options:

env({
  prefix: "APP_", // optional, default: undefined
  delimiter: "__", // optional, default: "__"
  forceCoerce: true, // optional, default: true
  renames: {
    APP_NESTED__KEY: "RANDOM_KEY", // optional
  },
});

prefix - prefix for env variable names. e.g., with prefix APP_, token becomes APP_TOKEN

delimiter - delimiter for nested keys. default: __

forceCoerce - boolean to force type coercion. default: true. e.g. if set to false, t.boolean() willn't coerce "true" to true and will return a parse error instead

renames - optional map of env variable names to schema paths. e.g., with renames: { APP_NESTED__KEY: "RANDOM_KEY" }, the env variable RANDOM_KEY instead of APP_NESTED__KEY

Errors

With APP_PORT=abc, prefix: "APP_" and a numeric port schema:

Config parsing failed with 1 issue(s):
- APP_PORT from env: expected number

ParseConfigError.issues preserves the validation message and full field path, with source and the environment key. Missing required values are reported against the final defaults source.