Local-first: nothing you paste ever leaves your browser
The home of digital signatures.
ECDSA signs most of the modern internet — TLS, SSH, JWTs, passkeys, Bitcoin and Ethereum. When a signature refuses to verify, this is where you debug it: free tools that auto-detect curves, formats and encodings, and explain what is actually wrong.
Detected locally in your browser — nothing you paste leaves the page.
- 13
- free tools
- 100%
- client-side crypto
- 0
- accounts required
- 2035
- NIST draft horizon
no paywall, no trial
WebCrypto in your browser
open a tool and paste
classical signatures disallowed
Signature Lab
Every tool works offline-grade: pure client-side cryptography, no accounts, no telemetry on your data.
Signature Error Explainer
Diagnose why verification fails
Your signature looks valid but verification fails? Paste key, message and signature — the explainer tests common mismatch causes: wrong hash, wrong curve, encoding confusion, high-S, double hashing.
Open toolNonce Reuse Checker
Scan a Bitcoin address for repeated r values
ECDSA's one fatal mistake: signing twice with the same nonce reveals the private key. Paste a Bitcoin address — the checker scans its historical signatures for repeated r values, the fingerprint of nonce reuse.
Open toolOpenSSL Command Builder
Build the openssl command you need
Pick a task — EC or RSA keys, self-signed certificates, CSRs, PKCS#12 bundles, signatures, TLS probes — fill in the blanks and copy a command that works, with every flag explained. Paste a command you found somewhere and it explains that too.
Open toolECDSA Signature Verifier
Verify any ECDSA signature
Paste a public key, message and signature — auto-detects curve (P-256, P-384, P-521, secp256k1), signature format (DER or raw) and encoding, then verifies locally in your browser.
Open toolJWT ES256 Debugger
Decode & verify ES256/ES384/ES512 tokens
Decode a JWT, inspect header and claims, verify ECDSA-signed tokens (ES256, ES384, ES512) against a public key, and get a plain-English explanation of what is wrong.
Open toolDER ⇄ Raw Converter
Convert signature formats
Convert ECDSA signatures between ASN.1 DER and raw r‖s (IEEE P1363) formats, inspect r and s values, and detect non-canonical high-S signatures.
Open toolX.509 Certificate Decoder
Inspect certificates
Decode a PEM or DER certificate: subject, issuer, validity, key algorithm and curve, signature algorithm, extensions — with notes on deprecated algorithms and post-quantum readiness.
Open toolTest Vector Generator
Generate keys & signatures for your tests
Generate reproducible ECDSA test vectors: key pairs, messages and signatures for any curve and hash, exported as JSON, JWK and PEM — including deliberately invalid vectors for negative tests.
Open toolSSH Key Inspector
Decode authorized_keys entries
Paste an OpenSSH public key or a whole authorized_keys file: key type, curve or size, SHA-256 and MD5 fingerprints, comments — with an assessment of deprecated key types.
Open toolLibrary Interop Cheatsheet
Why library A's signature fails in library B
An interactive matrix of how OpenSSL, Node.js, WebCrypto, Go, Python and Java handle ECDSA: default signature formats, high-S policy, deterministic nonces — pick a signer and a verifier to get a compatibility checklist.
Open toolJWKS & OIDC Checker
Check the key set behind your tokens
Enter a JWKS URL, an OpenID configuration or just the issuer domain — the checker fetches what your provider actually serves and reports key sizes, kid coverage, duplicate identifiers, expired certificates, private material published by mistake, and the algorithms advertised.
Open toolWebAuthn / Passkey Inspector
Decode passkey registration & login
Decode what the browser returns from navigator.credentials.create() and .get(): clientDataJSON, attestation object, authenticator data flags bit by bit, AAGUID, credential ID and the COSE public key — then verify the login signature locally.
Open toolElliptic Curve Playground
See the math behind the signatures
An interactive visualization of an elliptic curve over a small prime field: point addition, scalar multiplication and why reversing it is hard — the intuition behind every ECDSA key.
Open toolHow the Lab works
Built like a workbench, not a web service: the page is the whole machine.
- 01
Paste your material
A public key, a JWT, a certificate, a stubborn signature — whatever refuses to verify. No sign-up, no upload button.
- 02
Analyzed in your browser
Curves, formats and encodings are auto-detected and checked with WebCrypto, right in the tab. The network stays silent.
- 03
An answer, with the why
Not just valid or invalid — the tools test the usual mismatch causes and explain the actual mechanism, in plain English.
New research · 500 domains measured
The State of Signatures on the Web
We scanned the busiest sites on the internet with the same engine that powers our domain grader. RSA still outweighs ECDSA 62/38, a quarter of them still answer a TLS 1.0 handshake, and barely one percent would survive the 47-day certificate limit arriving in 2029. Charts, methodology and the raw data are all public.
Read the reportBeyond the Lab
Two bigger checks for the things you run in production:
Domain check
Signature Health: grade your domain A–F
Certificate chain, key algorithms, protocol floor, the new 47-day lifetime rules and post-quantum readiness — one scan, one letter, a README badge and free expiry alerts.
10 questions
PQC Migration Planner
Answer ten questions about your stack and get a prioritized post-quantum migration plan against the NIST draft timeline — built locally, exportable as Markdown or PDF.
NIST IR 8547
ECDSA has a retirement date.
NIST's draft transition plan would disallow today's elliptic-curve and RSA signatures after 2035, in favor of post-quantum algorithms. Meanwhile, TLS certificate lifetimes are shrinking from 200 days (2026) to 47 days (2029). Knowing exactly where and how your systems sign things stops being optional well before either date.
Countdown to 2035
…until NIST IR 8547 (initial public draft) would have classical signature algorithms — ECDSA, EdDSA and RSA, at every key size — disallowed for federal use. That is the date P-256 and RSA-3072 are measured against.
One earlier step, ~— years out: 112-bit parameter sets — RSA-2048 and P-224 — are deprecated after 2030, meaning still usable but carrying acknowledged risk. Planned, not urgent — but the inventory that makes either date manageable takes longer to build than the swap itself.
Learn
The concepts behind the tools — short, precise, and free of hand-waving.
Algorithms
ECDSA vs RSA
Key and signature sizes at equal security, signing and verification speed, where each runs the internet — and what the NIST post-quantum deadlines mean for both.
Read articleJWT
ES256 vs RS256
What the JWT alg values actually mean, why token size differs 3×, why verifiers must pin an algorithm allowlist, and why alg:none is never acceptable.
Read articleFormats
ECDSA signature formats
One signature, two encodings: ASN.1 DER vs raw r‖s at the byte level, high-S vs low-S normalization, and a comparison of library defaults.
Read articleFree course · 7 lessons
Signatures by Hand
Learn ECDSA by computing it. Add points on a tiny curve, derive a public key, produce a signature by hand — then do the real thing on P-256 and diagnose one that fails.
What's next
The Lab is step one. We are building the platform around it:
Available now
Repository scanner
A zero-dependency CLI that maps every place your code signs or verifies: libraries, curves, key handling, JWT configuration — with findings ranked by confidence. Text, JSON and SARIF output.
npx ecdsa-scan . →In development
Signing inventory
One map from repository to key to environment: which keys exist, what they sign, which algorithms they use, and what needs to migrate before the post-quantum deadlines.
Planned
Runtime monitoring
Read-only integrations with AWS KMS and Vault that turn raw signing events into a clear picture: which key signed what, from where, and under which policy.