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Showing the 23,775 endpoints that answered our last unpaid knock, most recently knocked first. The catalogue holds 91,887 listings in all: 22,941 charge, 895 answered without asking, 10,293 did not reach a working endpoint, and 57,758 we have never knocked on. Type something above to search all of them.
Ohm's law and power: give any two of voltage, current, resistance and power and get all four, with engineering units.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Multiply two matrices (up to 10x10) given as JSON, with shape check and the product matrix.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Wave speed, frequency and wavelength, plus the Doppler-shifted frequency for sound (moving source or observer) or light.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Add, average or subtract sound levels in dB: total of several sources, N identical sources, or background-corrected level.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Loudness maths: gain to a LUFS target or platform, resulting true peak vs ceiling, or combining segment loudness.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Validate an ISBN-10 or ISBN-13 check digit and convert between the two forms.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Round a price to a charm ending such as .99 or .95, or to steps like 9 at the end of tens, up, down or nearest.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Encode or decode text as base64, base64url, hex, URL percent-encoding or HTML entities; invalid input is reported, not guessed.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Normalise country names like USA, U.S. or United States of America to ISO codes; up to 25 per call, with confidence.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Pearson and Spearman correlation of two lists with p-values, plus the least-squares line, R squared and an optional prediction.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Shift a key by semitones with the right sharp or flat spelling, its relative major or minor, signature and capo shapes.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Normalize a URL: lowercase host, default port and fragment removed, sorted query, tracking parameters stripped.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Closest known exoplanets to the Sun in light-years, optional size filter, with star type, orbit and habitable-zone position.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Space weather right now: NOAA G, S and R scale levels now, 24-hour max and 3-day outlook, with a calm/active/storm verdict.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Vigenere cipher encode or decode with a key, or estimate the key length of a ciphertext by index of coincidence.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Minimum handheld shutter speed (reciprocal rule) and the longest star-point exposure by the 500 rule and the NPF rule.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Room air-conditioner BTU from floor area (ENERGY STAR chart), tons, and an under- or over-sizing check against a load.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Body mass index from weight and height, metric or imperial, with the WHO adult category and the 18.5 to 24.9 weight range.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
One validator: its status, balance and activation window. PulseChain (chain id 369). $0.003 USDC per call.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
City or place profile from Wikidata: coordinates, population, country, elevation, time zone, with property ids.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Decode a geohash to its center latitude/longitude, bounding box and the plus-or-minus error in degrees.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Exact pmf, cumulative and tail tables for geometric, negative binomial, hypergeometric, binomial and Poisson.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Ellipsoidal (WGS84, Vincenty) distance and bearings between two points, compared with haversine on a sphere.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Validate a Bitcoin mainnet address and report its type, confirmed and pending balance, transaction count and USD value.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Print book spine width in inches and mm from page count and paper type (white, cream, color) or your own thickness.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Resolve a species name (typos, old synonyms) to its accepted scientific name and full taxonomy, with match confidence.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Nearest standard E6, E12, E24, E48, E96 or E192 resistor values to a target, with the percent error of each neighbour.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Size a rooftop solar system from annual kWh and peak sun hours: kW, panel count, yearly output, savings and simple payback.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
US M2 money stock, monthly, in billions of dollars (seasonally adjusted), with the latest value, prior month, month-over-month and year-over-year change, and recent history. No ticker needed. A liquidity gauge watched for inflation and risk-asset context. Sourced from the St. Louis Fed (FRED). From x402stock, a pay-per-call market & economic data API. Pay per request in USDC via x402, no API key.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Grade a domain's email authentication: SPF and DMARC records parsed, policy strength, and spoofing exposure.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Ordinal suffix and word for a number: 1st/2nd/3rd/11th, French 1er/2e, Spanish 1.º/1.ª, German 1. with the word form.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Lease versus buy over the lease term: lease payment from money factor and residual, loan payment, resale equity and net cost.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Working hours between two timestamps under a weekly schedule with breaks and a holiday list.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Baking pan volume in cups and mL for round, square and rectangular pans, and the recipe scale factor from one pan to another.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Units needed for a peak load at a target utilisation plus N+k redundancy, utilisation after failures, and growth projection.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
SWR, reflection coefficient, return loss, mismatch loss and reflected power from SWR, a resistive load, or two power readings.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
IANA service name and common use for a TCP/UDP port (about 130 well-known ports), plus the port range class.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
License of a package version classed as permissive, weak, strong or network copyleft, with commercial-use notes.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Perp order-book depth and market-order slippage for $10k and $100k on Hyperliquid, with a thin/deep verdict.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Print size from image pixels at a DPI, or the pixels and megapixels needed for a print size; with viewing-distance advice.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Is a coin a live Hyperliquid perp? Listed, delisted or isolated-only, with max leverage and size precision.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Modular exponentiation base^exp mod m for big integers, decimal or 0x hex, up to 4096 bits.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Cricket batting average and strike rate, or bowling economy, average and strike rate, from raw career or match numbers.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Matrix determinant, inverse, transpose, rank, trace, product with a second matrix, and eigenvalues of 2x2 and 3x3 matrices.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Expected value, variance, standard deviation and chance of profit for a list of payoffs with probabilities or weights.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
NWS wind chill (feels-like in cold wind) from temperature and wind speed in F and C, with frostbite timing when severe.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Convert a domain to punycode (xn--) or back to Unicode label by label per RFC 3492, flagging mixed scripts.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Global crypto market stats (CoinGecko): total market cap, 24h volume, BTC/ETH dominance, active coins. No params. Use when an agent needs a one-call market overview.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Registration facts for a domain from RDAP: registrar, created, expires, status and nameservers, with age and expiry flags.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
Parse a gzip header: method, flags, modification time, original file name, OS and compression hint.
The price is the seller’s own listing. it demanded payment when we knocked, on 2026-10-25.
The description and the price are the SELLER’S, copied from their listing and not checked by us. The badge is OURS and is one unpaid handshake: “answered unpaid” means it answered us once without asking for payment, which is not a standing offer, and an unpriced listing is unpriced rather than free.
Knocking goes to the knock page, which reads the terms live before anything is signed. A listing can be out of date in both directions, which is the reason to knock rather than to read a row.