Number Base Converter — BigInt-Exact, Bases 2-36, Two's Complement

Convert numbers between any bases 2-36 with arbitrary precision — values beyond 2^53 convert exactly (BigInt throughout, never a float in sight). Standard prefixes (0x, 0o, 0b) just work, negatives get two's-complement views at 8/16/32/64 bits, and every record includes all common bases at once. Up to 50 conversions per run, online, by API, or as an agent tool via Apify MCP.

The precision point is the product: most online converters silently corrupt anything past 15-16 digits because they run on floats. 18446744073709551615 (2^64-1) converts here to exactly ffffffffffffffff — asserted by our release test.

What you get

• decimal / binary / octal / hex — always, plus toBaseValue for any explicit target base 2-36
• bitLength / byteLength — how wide the value really is
• twosComplement — for negatives, the 8/16/32/64-bit views (binary, hex, unsigned) where the value fits
• Prefix smarts: 0xff converts as hex without declaring fromBase (the prefix wins whenever its letter isn't a valid digit in the declared base — so base-34+ values containing literal x still parse correctly)
• Underscore separators accepted (1_000_000)
• Fail-soft: invalid digits for the declared base never fail the run — {ok: false, error} naming the bad digit, never charged.

Input

{ "value": "0xDEADBEEF" }

Bulk with explicit bases: { "items": [{ "value": "18446744073709551615", "fromBase": 10, "toBase": 16 }, { "value": "-42" }] }

Output (real run)

{
  "input": "0xDEADBEEF",
  "ok": true,
  "fromBase": 16,
  "decimal": "3735928559",
  "binary": "11011110101011011011111011101111",
  "octal": "33653337357",
  "hex": "deadbeef",
  "bitLength": 32,
  "byteLength": 4,
  "isNegative": false,
  "bases": { "2": "...", "8": "...", "10": "3735928559", "16": "deadbeef" }
}

-42 additionally returns twosComplement: { "8": { "binary": "11010110", "hex": "0xd6", "unsigned": "214" }, ... }.

Pricing

$0.0004 per number converted. No start fee. Invalid inputs are never charged.

No direct paid base-converter incumbent was found on the store (2026-08-07 search — results are file converters). Pricing is the cost-plus floor of our ladder, stated plainly.

Honest limits

• Integers only — fractional radix conversion is out of scope (a different, rarely-needed tool).
• Two's-complement views appear only at widths where the value fits; a number needing 70 bits shows no 64-bit view rather than a truncated lie.
• Digits are 0-9 then a-z (case-insensitive), standard for bases up to 36.

FAQ

Why does BigInt matter for a converter? Number("18446744073709551615") is already wrong before conversion begins (floats round past 2^53). Hashes, snowflake ids, and 64-bit registers all live past that line — this tool never touches floats.

How are negative numbers converted? The sign is preserved in the standard representations (-101010 in binary), and twosComplement gives you what the bits look like in fixed-width registers — the thing you actually want when debugging.

Does 0x work without fromBase? Yes — and the edge case is handled honestly: in bases 34-36 where x is a real digit, your declared base wins over the prefix.

Can I convert to base 36? Any target 2-36 via toBase; the four common bases are always included regardless.

Why did some rows come back ok: false? A digit wasn't valid for the declared base (e.g. XYZ in base 10) — the error names the exact digit. Never charged.

Use from code or AI agents

curl -s "https://api.apify.com/v2/acts/EliAI~number-base-converter/run-sync-get-dataset-items?token=$APIFY_TOKEN" \
  -X POST -H 'Content-Type: application/json' \
  -d '{"items": [{"value": "ff", "fromBase": 16}, {"value": "1010", "fromBase": 2, "toBase": 36}]}'

Agents: connect Apify MCP and call the EliAI/number-base-converter tool.

• Capability: BigInt-exact radix conversion (2-36) with prefixes, two's complement, bit widths
• Required input: value (or items array); optional fromBase/toBase
• Returns: one record per value with all common bases + optional target base
• Bounded: 50 conversions per run; failures isolate per value
• Side effects: none