Underscoredone

Sends a real request to any URL you provide, attaches an Origin header, and reads back all six standard cross-origin permission headers the server returns. Tells you whether cross-origin requests are enabled at all, whether your specific origin is permitted, and shows you every permission value exactly as the server sent it. Perfect for figuring out why a browser is blocking a request, confirming a freshly deployed service is configured correctly, or auditing whether a public API allows credentialed cross-origin calls.

Gives you official United States inflation numbers from the government's Consumer Price Index. Ask for the newest reading, a specific month in the past, or a whole range of months, and get back clear percentages for overall inflation and 'core' inflation (which ignores food and energy prices), plus a plain-English summary sentence.

Send an HTTP request to any URL from our servers and receive the full response — including the status code, all response headers, and the body content. Supports GET, POST, PUT, PATCH, DELETE, and HEAD. Automatically follows up to 3 redirects. Useful for testing endpoints, verifying servers are responding correctly, debugging redirect chains, or fetching raw data without needing a local setup.

Send up to 10 domain names and get back every DNS record type (A, AAAA, MX, CNAME, TXT, NS, PTR, SOA, SRV, CAA, NAPTR, DS, TLSA) plus the full WHOIS registration profile (registrar, dates, contacts, status, nameservers) for each one. URLs are accepted and automatically stripped down to the bare domain. Duplicate domains are quietly removed before processing. Results come back as one flat row per domain, ready to drop into a spreadsheet, database, or pipeline.

Send a list of domain names and this tool tells you exactly how old each one is, when it was first registered, when it expires, and how much time is left before expiration. Great for spotting brand-new suspicious domains, researching competitors, or evaluating domains before buying or linking to them. Works with over 100 domain extensions worldwide.

Give this API up to 10 domain names and it will tell you whether each one has a registration record on file with the official registry. It uses RDAP — the modern, structured replacement for WHOIS — so there is no messy free-text parsing. Each domain comes back labeled 'registered', 'unregistered', or 'indeterminate' (when the registry does not support RDAP for that ending). Important: 'unregistered' means no record was found, which usually means the name is available — but reserved or premium names can also return no record. This API tells you registration status only; it does not tell you price, premium status, or whether a registrar will actually let you buy the name.

This tool reads live information from Hacker News, a popular website where people share and discuss technology news. You can either ask for a current list of stories (like the Top, New, Best, Ask, Show, or Job lists) or ask for every story, job posting, and poll that was posted on one specific calendar day in the past. You can also choose to pull in the discussion comments underneath each story, including nested replies several levels deep.

Give this API any text or binary data and it instantly returns its fingerprint under whichever hash algorithms you choose — SHA-256, SHA-512, MD5, BLAKE2, CRC32, and more. It also signs data with a secret key (HMAC) and, most importantly, safely verifies whether an incoming signature matches — using a timing-safe comparison that prevents secret-leaking attacks. Language models cannot perform hashing: they produce a string of the right length and character set that looks correct but is simply wrong. Every webhook verification, idempotency key, cache fingerprint, or integrity check that relies on a hallucinated hash is silently broken. This API is the cure.

Give this API a list of up to 10 web addresses and it will visit each one to tell you whether it is working, broken, or redirecting visitors somewhere else. You get back the exact status number (like 200 for OK, 404 for not found, 500 for server error), whether the address redirects, and where it redirects to. Great for finding broken links, verifying website migrations, and running quick SEO audits without writing any code.

Every AI agent and developer runs into broken or confusing JSON constantly. This tool handles all the most common JSON headaches in one place: check if JSON is valid (with exact error location), fix near-JSON that has typos or formatting mistakes, pretty-print or minify, pull out specific values using a path expression, compare two JSON documents and see exactly what changed, convert to and from YAML or CSV, produce a byte-stable canonical form for hashing or signing, validate against a schema, and get size and structure statistics. Same input always gives the same output — fully predictable, no side effects.

Give this API a loan amount, an interest rate, and a repayment term, and it hands back the precise monthly payment plus a complete schedule showing — for every single month — how much goes to interest, how much reduces the balance, and what you still owe. You can also ask 'what if I pay an extra $300 a month?' or 'what if I make a $10,000 lump payment in month 24?' and it will tell you exactly how many months you save and how much interest you avoid. Every number is computed with banker's rounding and a pinned arithmetic rule so that two correct systems running the same inputs produce identical results, down to the cent. No rate lookups, no market data — you supply the rate, the API does the math.

Give this API a hostname or IP address and it will try connecting to each port in your requested range. For every port that answers, it tells you whether it is open or blocked, which service is likely running there (like a web server or SSH), and what software version was detected. This saves you from installing network tools, parsing messy command-line output, or writing socket loops yourself. Only scan hosts you own or have permission to scan — this tool does not check that for you.

Send a list of texts — website addresses, phone numbers, plain words, WiFi details, anything — and get back a ready-to-use QR code image for each one. Every QR code comes as a base64-encoded PNG you can drop straight into a webpage or save to disk. Great for marketing campaigns, event tickets, product labels, menus, or any situation where you need many QR codes in one go. Empty entries are quietly skipped. Each input is limited to 700 characters. You must send at least one non-empty entry.

Give this API a web address and it will visit that page, then hand back everything an SEO professional needs to know: the page title, meta description, meta keywords, robots instructions, canonical link, H1/H2/H3 headings, how many links are on the page, and the HTTP status code. No setup required — just paste a URL and get structured data back in under two seconds.

Give this API a link to any website's sitemap.xml file and it will fetch and parse it, returning every URL found inside. If the sitemap links to other sitemaps (called sitemap indexes), it will follow and extract those too. Each URL is returned with any extra information available, such as when the page was last updated and how often it changes. Useful for SEO audits, content inventories, broken link checks, and competitive research.