MCP Server: io.github.zvmzaretsky/utility-belt

This Model Context Protocol (MCP) server, io.github.zvmzaretsky/utility-belt, provides 13 deterministic agent utilities for tasks such as timezone, cron, RRULE, currency, regex, diff, hashing, and more. The server’s focus is utility functions intended for consistent, predictable results.

🛠️ Key Features

13 deterministic agent utilities
Includes timezone, cron, RRULE, currency, regex, diff, hashing

🚀 Use Cases

Agent workflows requiring timezone and scheduling logic (cron, RRULE)
Data processing and validation using currency, regex, diff, and hashing utilities

⚡ Developer Benefits

Deterministic behavior for repeatable utility execution
Broad utility coverage for common agent-side operations

⚠️ Limitations

Server description provided does not include specific tool names/count beyond the total of 13, or any additional operational constraints

FabTally Utility Belt — MCP server

The deterministic micro-utilities AI agents call constantly, as an MCP server (stdio + streamable-HTTP) and a pay-per-call HTTP API. One reliable bundle instead of thirteen flaky npm deps.

Free tools return real results with no wallet: convert, text, hash, encode, id, regex.
Paid tools ($0.001/call, x402 · USDC on Base): timezone, cron, rrule, currency, diff, jsonschema, datemath. With no payment a paid tool returns the decoded x402 402 challenge (price / network / asset / payTo) so an agent can pay and retry with x_payment. Humans can instead prepay by card and use an X-FabTally-Key credit key against the HTTP API.

This server holds no private key. It fronts https://belt.fabtally.com. Every utility is a pure, deterministic function with strict input validation; bad input → 400, never charged; nothing is stored.

Tools

Tool	Tier	What it does
`convert`	free	Unit conversion (length/mass/temperature/volume/data/time/area/speed/angle/pressure/energy).
`text`	free	slugify · case-convert (camel/pascal/snake/kebab/constant/…) · `{{template}}` fill.
`hash`	free	sha256/sha512/sha384/sha1/md5/sha3-256/keccak256/ripemd160, optional HMAC, hex/base64 out.
`encode`	free	base64 / base64url / hex / url / html encode & decode.
`id`	free	uuid v4/v7, ULID, nanoid, random hex/base64url/int (count up to 1000).
`regex`	free	test/match/extract/replace with catastrophic-backtracking protection (killable worker + timeout).
`timezone`	$0.001	Instant → IANA zone with historically-correct DST; offsets, abbreviations, DST flags.
`cron`	$0.001	Cron expression → next N run times + plain-English description.
`rrule`	$0.001	iCal RRULE (RFC 5545) → next N occurrences.
`currency`	$0.001	Live currency conversion at reference/mid-market rates (keyless ECB feed, cached).
`diff`	$0.001	Text diff: unified patch + structured op-list + add/remove/hunk stats.
`jsonschema`	$0.001	Validate against JSON Schema (draft 2020-12) and explain every error in plain English.
`datemath`	$0.001	Add/subtract ISO-8601 durations, diff into chosen units, business-day add/diff.

Install / run

stdio (Claude Desktop, Cursor, any MCP client)

jsonc

// claude_desktop_config.json
{
  "mcpServers": {
    "fabtally-belt": { "command": "npx", "args": ["-y", "fabtally-belt-mcp"] }
  }
}

Or clone and run: node index.js (speaks MCP over stdio).

streamable-HTTP (remote)

Hosted: https://belt.fabtally.com/mcp. Or self-host: MCP_HTTP_PORT=8108 node http.js.

Config

FABTALLY_BELT_BASE — API base (default https://belt.fabtally.com).

Paying for paid tools

A paid tool with no x_payment returns:

json

{ "payment_required": true, "http_status": 402,
  "challenge": { "x402Version": 2, "accepts": [ { "scheme": "exact", "network": "eip155:8453",
    "amount": "1000", "asset": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913", "payTo": "0x…" } ] } }

Build an x402 payment authorization (EIP-3009 transferWithAuthorization to payTo) for the accepts entry and call the tool again with the token in x_payment. amount is atomic USDC (1000 = $0.001).

Guarantees

Deterministic. Stateless — no PII or request data stored. Receive-only wallet (no custody). Currency figures are reference/mid-market rates for informational use, not a dealable quote. MIT licensed.

value	number	required	Numeric value to convert.
from	string	required	Source unit, e.g. c, km, GiB, gal, kg.
to	string	required	Target unit in the same dimension.

op	string	required	slugify \| template \| camel \| pascal \| snake \| kebab \| constant \| dot \| path \| title \| sentence \| upper \| lower
text	string	optional	Input text for slugify/case ops.
template	string	optional	Template string for op='template', with {{key}} placeholders.
data	object	optional	Object of values for op='template'.
separator	string	optional	Slug separator (default '-').
strict	boolean	optional	template: throw on missing keys.

algorithm	string	required	sha256 \| sha512 \| sha384 \| sha1 \| md5 \| sha3-256 \| keccak256 \| ripemd160
text	string	required	Input to hash.
input_encoding	string	optional	How `text` is encoded: utf8 (default) \| hex \| base64 \| base64url.
output_encoding	string	optional	Digest encoding: hex (default) \| base64 \| base64url.
hmac_key	string	optional	If set, compute HMAC with this key (not for keccak256/sha3-256).

kind	string	optional	uuidv4 (default) \| uuidv7 \| ulid \| nanoid \| hex \| base64url \| int
count	integer	optional	How many to generate (1-1000, default 1).
size	integer	optional	nanoid length (default 21).
bytes	integer	optional	hex/base64url random byte length (default 16).

pattern	string	required	The regular expression source (max 2000 chars).
input	string	required	The text to run it against (max 200k chars).
flags	string	optional	Any of g,i,m,s,u,y.
op	string	optional	test \| match \| extract (capture groups) \| replace. Default match.
replacement	string	optional	Replacement string for op='replace' (supports $1 etc.).
limit	integer	optional	Max matches for global ops (default 1000).

op	string	required	base64-encode\|base64-decode\|base64url-encode\|base64url-decode\|hex-encode\|hex-decode\|url-encode\|url-decode\|html-encode\|html-decode
text	string	required	Text to encode/decode.

datetime	string \| number	required	Instant to convert: ISO 8601 (e.g. 2021-03-14T01:30:00) or epoch seconds/millis.
from_zone	string	optional	Source IANA zone (default UTC), e.g. America/New_York.
to_zone	string	required	Target IANA zone, e.g. Europe/London, Asia/Tokyo.
x_payment	string	optional	x402 payment payload (base64) for this PAID tool. If supplied it is forwarded as the X-PAYMENT header to settle the $0.001 call and return the real result instead of a 402 challenge. Omit to get the price challenge first.

expression	string	required	Cron expression, e.g. '0 9 * * 1-5'.
timezone	string	optional	IANA timezone (default UTC).
count	integer	optional	How many upcoming runs (1-100, default 5).
from	string	optional	Compute runs after this ISO datetime (default now).
x_payment	string	optional	x402 payment payload (base64) for this PAID tool. If supplied it is forwarded as the X-PAYMENT header to settle the $0.001 call and return the real result instead of a 402 challenge. Omit to get the price challenge first.

rrule	string	required	RRULE string, optionally with a DTSTART line.
after	string	optional	Return occurrences after this ISO datetime (default now).
count	integer	optional	How many occurrences (1-366, default 5).
timezone	string	optional	Render occurrences in this IANA zone.
x_payment	string	optional	x402 payment payload (base64) for this PAID tool. If supplied it is forwarded as the X-PAYMENT header to settle the $0.001 call and return the real result instead of a 402 challenge. Omit to get the price challenge first.

amount	number	required	Amount in the source currency.
from	string	required	Source ISO-4217 code, e.g. USD.
to	string	required	Target ISO-4217 code, e.g. EUR.
x_payment	string	optional	x402 payment payload (base64) for this PAID tool. If supplied it is forwarded as the X-PAYMENT header to settle the $0.001 call and return the real result instead of a 402 challenge. Omit to get the price challenge first.

a	string	required	Original text.
b	string	required	Changed text.
mode	string	optional	lines (default) \| words \| chars.
context	integer	optional	Unified-diff context lines (default 3).
label_a	string	optional
label_b	string	optional
x_payment	string	optional	x402 payment payload (base64) for this PAID tool. If supplied it is forwarded as the X-PAYMENT header to settle the $0.001 call and return the real result instead of a 402 challenge. Omit to get the price challenge first.

schema	object	required	A JSON Schema (draft 2020-12) object.
data	any	optional	The value to validate against the schema.
x_payment	string	optional	x402 payment payload (base64) for this PAID tool. If supplied it is forwarded as the X-PAYMENT header to settle the $0.001 call and return the real result instead of a 402 challenge. Omit to get the price challenge first.

op	string	required	add \| subtract \| diff \| business-add \| business-diff
date	string	optional	Base date for add/subtract/business-add (ISO 8601).
duration	any	optional	ISO-8601 duration string or object for add/subtract.
from	string	optional	Start datetime for diff/business-diff.
to	string	optional	End datetime for diff/business-diff.
units	any	optional	diff units, e.g. ['days','hours'].
days	integer	optional	Business days to add (business-add; may be negative).
holidays	array	optional	ISO dates to skip as holidays.
weekend	array	optional	Weekend weekdays (1=Mon..7=Sun; default [6,7]).
timezone	string	optional	IANA zone for parsing/rendering.
x_payment	string	optional	x402 payment payload (base64) for this PAID tool. If supplied it is forwarded as the X-PAYMENT header to settle the $0.001 call and return the real result instead of a 402 challenge. Omit to get the price challenge first.

MCP Server: io.github.zvmzaretsky/utility-belt

🛠️ Key Features

🚀 Use Cases

⚡ Developer Benefits

⚠️ Limitations

convert

text

hash

encode

id

regex

timezone

cron

rrule

currency

diff

jsonschema

datemath