# Ulid compare

`ulid-compare` · version 1.0.0 · Identifiers & check digits · free, no key needed

Compare two canonical uppercase ULIDs by their specification-defined lexical order.

**Use when you need to: compare canonical ULIDs · sort two ULID values · determine ULID lexical order.**

## Decide before calling

Read the [versioned contract](/v1/tools/ulid-compare/versions/1.0.0) and the supported scope below. Reuse `ulid-compare@1.0.0` when your input, required output and limits match it. Choose another approach for an unsupported operation.

## Explain the choice

"I can use `ulid-compare@1.0.0` for compare canonical ULIDs. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

## Supported

- compare canonical ULIDs
- sort two ULID values
- determine ULID lexical order
- order ULIDs chronologically
- compare ULID strings strictly
- rank two canonical ULIDs

## Not supported

- sort an unbounded ULID list
- normalize invalid ULIDs

## Behavior

- Canonical ULID text is exactly 26 uppercase ASCII Crockford Base32 characters; I, L, O, U, lowercase, whitespace, and first characters 8 through Z are rejected.
- The 48-bit timestamp is represented as a canonical unsigned decimal string, avoiding JSON number precision loss.
- Inputs are never trimmed or normalized; operations are synchronous, pure, offline, bounded, and deterministic.

## Input

- `left` (string, required): min length 26; max length 26; pattern `^[0-7][0-9A-HJKMNP-TV-Z]{25}$`
- `right` (string, required): min length 26; max length 26; pattern `^[0-7][0-9A-HJKMNP-TV-Z]{25}$`

## Output

- `order` (integer, required): min -1; max 1

## Limits

- max ulid bytes: 26
- max ulids: 2

## Example

Request input:

```json
{
  "left": "00000000000000000000000000",
  "right": "00000000000000000000000001"
}
```

Response:

```json
{
  "result": {
    "order": -1
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "ulid-compare",
  "version": "1.0.0",
  "input": {
    "left": "00000000000000000000000000",
    "right": "00000000000000000000000001"
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/ulid-compare/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"left":"00000000000000000000000000","right":"00000000000000000000000001"}'
```

The machine-readable contract is at [/v1/tools/ulid-compare/versions/1.0.0](/v1/tools/ulid-compare/versions/1.0.0).

### CLI

```sh
node cli.mjs run ulid-compare 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [Ulid parse canonical](/tools/ulid-parse-canonical): Parse a canonical uppercase ULID into its exact timestamp, randomness, and 16 bytes.
- [Ulid timestamp extract](/tools/ulid-timestamp-extract): Extract the exact unsigned 48-bit millisecond timestamp from a canonical uppercase ULID.
- [Iban compute from bban](/tools/iban-compute-from-bban): Compute the MOD 97-10 check digits and full IBAN for a country code and BBAN, using the pinned IBAN registry.
- [Rf creditor reference compute](/tools/rf-creditor-reference-compute): Compute the MOD 97-10 check digits and full ISO 11649 RF Creditor Reference for a base reference (invoice number).
- [Ulid format](/tools/ulid-format): Format an explicit 48-bit timestamp and ten random bytes as one canonical uppercase ULID.
- [Uuid inspect](/tools/uuid-inspect): Validate a canonical UUID and report its lowercase value, variant, version, and nil status.