JWT Decoder – Inspect RS256 vs HS256 Tokens Offline
Securely decode JWTs locally. View header, payload, signature, check expiration, and understand RS256 vs HS256. No server, no logs, works in browser.
Master This Tool
Deep-dive guides and tutorials for advanced users.
RS256 vs HS256: Security and Implementation Guide
A deep dive into JWT signing algorithms. Learn why RS256 is the standard for production security and how FmtDev's local-first tools ensure Zero-Server-Logs privacy.
The Extension Sniffing Crisis: Why Developers are Moving to Local-First Tools
Browser extensions are silently sniffing development data. Learn why developers are moving to local-first, offline utilities like FmtDev Sovereign Suite.
The JSON-RPC Renaissance: Protocol Powering 2026 AI Agents
Discover why JSON-RPC 2.0 is the foundational protocol for AI agent tool calling and the Model Context Protocol (MCP) instead of REST or GraphQL.
The Shadow API Crisis: How Unmonitored Endpoints Break CORS & Auth
Discover how 'fast-shipping' AI agents create undocumented Shadow APIs. Learn why bypassing the API Gateway leads to CORS misconfigurations and JWT exploits.
Vector Dimensionality: Why Misaligned Embeddings Break RAG
Discover why projecting 3072-D embeddings into 1536-D indices destroys semantic retrieval. Learn to audit vector math using Cosine Similarity to prevent AI hallucinations.
The Dirty Secret of Dev Tools: Why Zero Server Logs is Mandatory
Pasting production JWTs or API keys into online formatters is a massive security breach. Discover why 100% offline, zero-server-log tools are the 2026 standard.
Securing AI Agents: How to Detect & Prevent Prompt Injection
A Cybersecurity Architect's guide to prompt injection in 2026. Learn about Token to Shell vectors, RAG poisoning, and embedding-based anomaly detection.
The Death of LocalStorage: Why Enterprise Apps Use Cookies
LocalStorage is an architectural liability. Learn why modern Next.js apps use HttpOnly cookies to prevent XSS token theft and secure account takeovers.
Understanding MCP Transport Layers: stdio vs. HTTP vs. WebSockets
A technical deep dive into Model Context Protocol (MCP) transport mechanisms. Compare stdio, HTTP with SSE, and WebSockets for secure AI agent integration.
PASETO vs JWT: 2026 Cryptographic Hardening
A technical deep-dive into why modern architectures are abandoning JWT for the deterministic security of PASETO v4. Analyze latency, memory usage, and algorithm confusion.
JWT vs Session: 2026 Guide to Scalable Auth
Compare stateless JWT vs stateful sessions for 2026. Analyze latency, memory consumption, and security risks like CSRF, XSS, and token revocation.
Where to Store JWTs: Cookie vs LocalStorage
Where should you store JWTs? Compare localStorage vs HttpOnly cookies. Learn why localStorage exposes you to XSS and how to secure your 2026 auth flow.
Fix TokenExpiredError: jwt expired & Invalid Signature
Learn how to fix TokenExpiredError: jwt expired, JWT Invalid Signature Error, and jwt malformed. Debug JWT issues locally and securely.
JWT Security: Algorithm Confusion & Secret Exposure
Understand the difference between JWT decoding and verification, and learn how to avoid the dangerous "alg: none" vulnerability.
How to Safely Decode JWTs Without Leaking Secrets
Many online JWT decoders are insecure. Learn why local decoding is the gold standard for developer security.