How do I decode a Base64 string online?

Paste your Base64 string into SmartDevBox at smartdevbox.com. It automatically detects Base64 encoding and decodes it instantly — no configuration needed.

How do I decode a JWT token without a secret?

Paste your JWT token into SmartDevBox. The JWT Inspector tool decodes the header and payload and displays them as readable JSON. Note: this decodes but does not verify the signature — you don't need the secret to read the claims.

How do I format or pretty-print JSON?

Paste your minified or unformatted JSON into SmartDevBox. The JSON Formatter tool detects it automatically and pretty-prints it with configurable indentation.

How do I convert a Unix timestamp to a human-readable date?

Paste a Unix timestamp (e.g. 1700000000) into SmartDevBox. The Unix Timestamp converter detects it and shows the equivalent date and time in UTC and your local timezone.

How do I convert JSON to CSV?

Paste a JSON array of objects into SmartDevBox and select the JSON → CSV tool. It converts your data to comma-separated format with headers derived from the JSON keys.

How do I compute a SHA-256 hash online?

Use the Hash Generator tool on SmartDevBox. Paste any text and it computes MD5, SHA-1, SHA-256, and SHA-512 hashes simultaneously in the browser.

How do I parse and understand a cron expression?

Paste your cron expression (e.g. "0 9 * * 1-5") into SmartDevBox. The Cron Job Parser explains it in plain English and shows the next scheduled run times.

How do I decode an X.509 certificate online?

Paste a PEM-encoded certificate (beginning with -----BEGIN CERTIFICATE-----) into SmartDevBox. The Certificate Decoder extracts and displays the subject, issuer, validity dates, public key, and extensions.

Is SmartDevBox free to use?

Yes. SmartDevBox is completely free with no account or sign-up required. All tools run in the browser. An optional AI mode (for ambiguous input detection) can be enabled with your own OpenAI API key.

Does SmartDevBox send my data to a server?

No. All tools run entirely in the browser using client-side JavaScript. Your data never leaves your machine unless you opt into the AI mode, which sends input to OpenAI for format detection.

JWT Encoder — Create & Sign JWT Tokens Online

JWT Encoder lets you build and sign JSON Web Tokens directly in your browser. Provide a JSON payload and a secret key, choose your HMAC algorithm (HS256, HS384, or HS512), and receive a signed JWT. The Web Crypto API handles all signing locally — your payload and secret are never transmitted to a server. The output panel shows the full token alongside the decoded header and payload for easy verification.

Common Use Cases

Generating test tokens for JWT-protected API endpoints
Creating tokens for development and staging environments
Testing how your application handles different claims (exp, iss, sub)
Learning and experimenting with JWT structure and signing

Frequently Asked Questions

Which JWT signing algorithms does SmartDevBox support?

SmartDevBox supports HMAC-based symmetric algorithms: HS256 (HMAC-SHA256), HS384 (HMAC-SHA384), and HS512 (HMAC-SHA512). Asymmetric algorithms (RS256, ES256) are not yet supported.

What payload format does the JWT Encoder expect?

The payload must be a valid JSON object. For example: { "sub": "user123", "iat": 1700000000, "exp": 1700003600 }. The iat (issued-at) claim is added automatically if not included.

Privacy & Security

This tool runs entirely in your browser using client-side JavaScript. No data is sent to a server — your input never leaves your machine. SmartDevBox has no account system, no usage tracking, and no paid tier. See the Privacy & Security page for full details.

JWT DecoderDecode JWT tokens and inspect header, payload, and signature instantly. Free, no sign-up. Works without the signing secret. 100% client-side.
Base64 DecoderDecode any Base64 string back to plain text instantly in your browser. Free, no sign-up, 100% client-side. Supports standard and URL-safe Base64.
Hash GeneratorCompute MD5, SHA-1, SHA-256, and SHA-512 hashes for any text. Free, no sign-up, 100% client-side.
JSON FormatterFormat and pretty-print JSON instantly in your browser. Validates syntax and shows error location. Free, no sign-up, 100% client-side.