Address checksum (EIP-55). Validate an EVM address and return its EIP-55 checksummed form, saying whether the input was all lower case, all upper case, correctly checksummed or mixed case with a wrong checksum (a likely typo). Works for every EVM chain. Use before sending funds or storing an address; for whether it is a contract use <chain>_is_contract.

Loan and mortgage calculator. Monthly payment of an amortised loan or mortgage from the amount, the annual interest rate and the term, plus the total paid, the total interest and the first months of the repayment schedule (principal, interest and balance). Fixed rate, monthly payments. Use to compare loan offers or plan a mortgage.

Decode calldata. Decode EVM transaction calldata into the function and its arguments with viem: give the function signature (transfer(address,uint256)), or leave it out to try common ERC-20, ERC-721, ERC-1155, WETH, permit and multicall functions by selector. Numbers come back as decimal strings. Use to read what a pending or past transaction does before signing; get calldata from eth_tx. A selector that does not match is 422, uncharged.

Distance between coordinates. Great-circle distance between two latitude/longitude points (haversine on the mean earth radius) in kilometres, miles and nautical miles, plus the initial compass bearing and the midpoint. Accurate to about 0.5% against the ellipsoid. Use for delivery radius, travel and proximity checks, or sorting places by distance; for coordinates of a place name use geocode first.

JSON to YAML. Convert a JSON value into a YAML document (block style, no line folding), for config files, Kubernetes manifests, GitHub Actions or docs that humans edit. Up to 100 KB of JSON. Use when a tool or person wants YAML; for the reverse use yaml_to_json. Invalid JSON is a 400, uncharged.

Tip calculator. Tip and total for a bill at a tip percentage, split between any number of people, optionally rounding each share up to the next whole amount. Use for receipts, expense apps and group payments.

Regex tester, test. Run a JavaScript regular expression against a text and return every match with its index and capture groups (named groups included). Pattern up to 300 characters, text up to 5,000; patterns with nested quantifiers such as (a+)+ are refused as unsafe, uncharged. Use to check a pattern before using it in code.

Language detection. Detect which language a text is written in: the most likely language with its ISO 639-3 and 639-1 codes and English name, plus the next candidates with relative scores, using trigram statistics for 82 major languages (franc-min). Works best above about 20 characters; very short or mixed text returns und (undetermined). Local, no outside service. Use to route messages, pick a translation target or filter content by language.

Caesar cipher, ROT13. Encode or decode text with a Caesar cipher: every letter A-Z shifted by 1-25 places (13, the default, is ROT13), case kept, digits and punctuation untouched. decode=true shifts back. Use for puzzles, spoiler hiding and teaching; it is not encryption.

Block number, Unichain. Latest block number and block details on Unichain, or any block by decimal number: hash, timestamp, transaction count, gas used and limit, base fee in gwei and producer. Use for timestamps and confirmation counts; for current fees use unichain_gas. A block that does not exist yet returns 404, uncharged.

Lorem ipsum generator. Lorem ipsum placeholder text: 1-20 paragraphs of 1-10 sentences, starting with the classic "Lorem ipsum dolor sit amet". The same seed always gives the same text. Use to fill mock-ups, templates and test data.

Phone number validation. Validate and format a phone number with the libphonenumber rules: whether it is valid and possible, the E.164 form, international and national formatting, country, calling code and line type (mobile, fixed-line, toll-free, VoIP…). Give +country code, or a national number and a two-letter country. Offline: nothing is sent and it does not say the line is in service. Use to clean contact lists or check a number before an SMS.

QR code generator. Generate a QR code for a URL or any text (UTF-8, up to 1,000 characters) as a scalable SVG plus a ready-to-embed data URL, at error correction L, M (default), Q or H. Use to put a link, Wi-Fi string or payment request on a page, label or ticket.

YAML to JSON. Convert a YAML document (config files, Kubernetes manifests, OpenAPI specs, front matter) into JSON, parsed by the yaml library with anchors and aliases resolved (alias expansion capped against billion-laughs documents) and duplicate keys refused. Up to 100 KB. Use before feeding YAML into a JSON-only tool or schema check; for the reverse use json_to_yaml. Invalid YAML is a 400 with the parser's message, uncharged.

User agent parser. Parse a User-Agent string into browser and version, operating system and version, device type (desktop, mobile, tablet or bot) and, for crawlers, which bot it is: Googlebot, Bingbot, GPTBot, ClaudeBot, PerplexityBot, social previewers, SEO crawlers and HTTP libraries such as curl or python-requests. Local rules, no outside service. Use to read access logs, segment traffic or spot AI crawlers.

Token allowance, Avalanche. ERC-20 token allowance on Avalanche: how much a spender may move from an owner's wallet (allowance), raw and in token units, and whether the approval is unlimited. Use to check an approval before a swap or to audit risky open approvals; for the owner's balance use avax_token_balance. Token is a ticker (USDC, USDT, WETH…) or a 0x contract; a missing contract is 404 and a non-ERC-20 422, both uncharged.

Avalanche gas price. Current gas price on Avalanche (eth_gasPrice): gas price, base fee and suggested priority fee in gwei, plus what a plain AVAX transfer (21,000 gas) costs right now. Takes no input. Use before sending a transaction or to decide whether to wait; for the fee a past transaction actually paid use avax_receipt.

Eth call, Avalanche. Read-only contract call on Avalanche (eth_call): send ABI-encoded calldata to a contract at the latest block and get the raw return data, without a transaction or gas. Use to read any view function that has no dedicated tool (the example reads USDC totalSupply, selector 0x18160ddd); decode the result with the function's ABI. Calldata up to 8 KB; a call that reverts is 422 with the reason, uncharged.

NFT owner, Avalanche. Owner of an NFT on Avalanche: the wallet that holds one ERC-721 token id right now (ownerOf), plus the collection's name and symbol. Use to verify who holds an NFT before a trade, a mint gate or an airdrop; for how many a wallet holds use avax_nft_balance, for the token's metadata avax_nft_metadata. A missing contract is 404, a token that does not exist 422, both uncharged.

Avalanche account nonce. Read the transaction count (nonce) of a 0x address on Avalanche, both confirmed and including pending transactions. Use to build the next transaction or to tell whether an address has ever sent anything; for its balance use avax_balance. A malformed address is rejected with 400, uncharged.