JWT validator, verifier and decoder

Paste a JSON Web Token to inspect its header and payload locally, validate its structure, then verify HMAC signatures when you have the secret.

Verification status

Paste a token and secret to verify.

Decoding only reveals claims. Trust the token only after a valid signature and expiration check.

Header


            
          

          

            
Payload

            

            
          

        

      

    


    
How to use this tool
Paste a token and select Decode token to inspect its header and claims. To verify an HMAC signature, enter the shared secret, choose the expected algorithm and select Verify signature.
Try it: Load example then Decode token to view the public HashyTools claim. This example has no valid signature: decoding must still show “Signature not verified yet”.
Limit: Decoded claims are untrusted. Verification supports HS256, HS384 and HS512 and the existing time checks; it does not validate issuer, audience, revocation or your application authorization rules.

      

        
JWT structure at a glance

        

          JSON Web Tokens package authentication claims into a compact string separated by dots. Each segment is Base64URL encoded,
          which is why you can decode the header and payload without hitting external services.
        

      

      

        

          
            

              Segment
              Contains
              Example claims
              Security notes
            

          
          
            

              Header
              Algorithm (`alg`) and token type (`typ`).
              {"alg":"HS256","typ":"JWT"}
              Never accept "alg":"none" in production.
            

            

              Payload
              Claims about the subject, issuer, scopes.
              {"sub":"123","exp":1700000000}
              Visible to anyone with the token. Do not store secrets here.
            

            

              Signature
              HMAC or asymmetric signature over header+payload.
              HMACSHA256(base64Url(header).base64Url(payload), secret)
              Required to verify authenticity. Use the verifier above for HMAC-signed tokens.
            

          
        

      

    


    

      

        
Best practices when working with JWTs

        

          Decoding claims is only the first step. Use these guidelines to keep tokens safe and your APIs predictable.
        

      

      

        

          
Always verify signatures

          

            Decode to inspect, but never trust claims until you validate the signature with the issuer's secret or public key.
          

        

        

          
Enforce expiry and audiences

          

            Reject expired tokens and ensure aud/iss claims match your application to prevent replay across
            services.
          

        

        

          
Avoid sensitive claims

          

            Anyone who obtains the JWT can read payload data. Store secrets server-side or encrypt the token with JWE when necessary.
          

        

      

    


    
What a valid JWT signature does and does not prove
Decode inspects public header and payload fields. Verify checks an HMAC signature only when you supply the matching secret.
  1. Use a development token signed with HS256, HS384 or HS512 and its test secret.
  2. Verify it, then change one payload character. Verification must fail.
  3. Check expiry, issuer, audience and application permissions in the receiving application.
A valid signature does not by itself authorize a request. RS256, ES256 and encrypted JWE are outside this verifier. Never treat decoded claims as trusted before verification.
JWT specification: RFC 7519


    

      
JWT decoder FAQ

      

        

          
What are the three parts of a JWT?

          

            A JWT contains a header, payload, and signature separated by dots. The header defines the algorithm, the payload carries
            claims, and the signature proves authenticity when verified with the correct key.
          

        

        

          
Does decoding a JWT verify its authenticity?

          

            No. Decoding only reveals the Base64URL-encoded JSON. Use the verifier with the issuer secret before you trust any claim in the payload.
          

        

        

          
What risks exist when handling JWTs?

          

            Tokens can leak sensitive information and be replayed if you skip expiration or revocation checks. Avoid logging JWTs and
            refuse tokens signed with weak secrets or the none algorithm.
          

        

        

          
Can I decode encrypted JWTs (JWEs) with this tool?

          

            No. The decoder targets signed JWTs (JWS). Encrypted JWEs require the decryption key and algorithms that are outside the
            scope of this page.
          

        

        

          
Does the decoder upload my tokens?

          

            No. HashyTools processes JWTs entirely on your device so your secrets and claims remain private.
          

        

      

    

      

    
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Run the AES interoperability guide or read how these tools are checked.