JWT0 (jwt0)

A command-line tool for inspecting and tampering with JSON Web Tokens (JWTs). Built for authorized security testing, CTF challenges, and debugging JWT handling in applications you own or have permission to test.

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Features

• Debug — decode and pretty-print a token's header and payload
• Bypass — generate tokens with the none algorithm (signature bypass)
• Confusion — perform RSA → HMAC algorithm confusion attacks
• Dict — brute-force HMAC secrets (HS256 / HS384 / HS512) using a wordlist (ships with an embedded common JWT secrets list; --file optional)
• Sign — re-sign a token with a known secret after tampering claims
• Verify — check if an HMAC secret matches a JWT signature
• Request — send HTTP requests with custom headers (curl-like), optional proxy / no-follow redirects

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Requirements

• Go 1.21+

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Installation

Clone the repository and build the binary:

git clone https://github.com/n0m-d/jwto.git
cd jwto
go build -o jwto ./cmd/jwto

Or use Make:

make build

Or use task:

task build

Or run directly without installing:

go run ./cmd/jwto <command> [flags]

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Usage

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                   - JWT0 - CLI Tool for JWT Tampering & Debugging -

usage: jwto [<flags>] <command> [<args> ...]

CLI Tool for JWT Tampering & Debugging


Flags:
  -h, --[no-]help          Show context-sensitive help (also try --help-long and --help-man).
  -j, --jwt=JWT            JWT to debug
  -c, --claims=CLAIMS ...  Payload claim key=value (infers bool/int/float/null; quote to force string)
      --claims-json=CLAIMS-JSON  
                           Payload claims as a JSON object (arrays/objects/typed values)
  -r, --delete_claims=DELETE_CLAIMS ...  
                           Delete Payload Claims

Commands:
help [<command>...]
    Show help.

bypass [<flags>]
    Bypass Signature Verification

debug
    Debug the provided token

confusion [<flags>]
    Algorithm Confusion Attack

dict [<flags>]
    Dictionary for Brute Force Attack

sign --secret=SECRET [<flags>]
    Sign the JWT with an HMAC secret

verify --secret=SECRET [<flags>]
    Verify HMAC secret against the JWT

request --url=URL [<flags>]
    Send an HTTP request (curl-like)

Most commands require a JWT via --jwt / -j. The request command does not need a JWT — pass tokens via headers instead.

Global flags

Flag	Short	Required	Description
--jwt	-j	Yes*	The JWT string to inspect or tamper with
--claims	-c	No	Add/overwrite claims as key=value (infers bool/int/float/null; quote to force string). Can be repeated
--claims-json		No	Claims as a JSON object (arrays, nested objects, explicit types)
--delete_claims	-r	No	Remove payload claims by name. Can be repeated
--help	-h	No	Show help

* Not required for request.

Claim flags are available on bypass, confusion, and sign.

--claims type inference:

Value	JSON type
true / false	boolean
null	null
1999999999	number (int)
3.14	number (float)
"true" / '123'	string (quotes stripped)
anything else	string

# Typed claims via -c
jwto -j "<TOKEN>" bypass -c admin=true -c exp=1999999999

# Force a string that looks like a bool/number
jwto -j "<TOKEN>" sign --secret "password" -c 'admin="true"'

# Arrays / nested objects
jwto -j "<TOKEN>" bypass --claims-json '{"admin":true,"roles":["user","admin"]}'

Commands

debug

Decode the token and display its raw string, segments, header, and payload.

jwto -j "<TOKEN>" debug

bypass

Strip or replace the signature to test servers that accept unsigned tokens or the none algorithm.

Flag	Default	Description
--alg	none	Signing algorithm: none, None, NONE, or default (keeps original)

jwto -j "<TOKEN>" bypass
jwto -j "<TOKEN>" bypass --alg=None
jwto -j "<TOKEN>" bypass -c admin=true -c role=admin -r exp
jwto -j "<TOKEN>" bypass --claims-json '{"admin":true,"nbf":null}'

Output is an unsigned token (header.payload.) with a trailing dot and no signature.

confusion

Re-sign an RSA JWT as HMAC using the RSA public key as the HMAC secret. Supports HS256, HS384, and HS512.

Flag	Required	Description
--pub_key	Yes	Path to the RSA public key file (PEM format)
--alg	No	HMAC algorithm: HS256, HS384, or HS512 (default: HS256)

jwto -j "<TOKEN>" confusion --pub_key ./wordlists/public.pem
jwto -j "<TOKEN>" confusion --pub_key ./public.pem --alg HS512
jwto -j "<TOKEN>" confusion --pub_key ./public.pem -c role=admin -r exp

dict

Brute-force the HMAC signing secret against a wordlist. Supports HS256, HS384, and HS512 only.

If --file is omitted, JWT0 uses a gzip-compressed common secrets list embedded in the binary (derived from wallarm/jwt-secrets). Pass --file for larger lists (e.g. rockyou).

Flag	Default	Description
--file	(embedded list)	Path to a wordlist (one candidate secret per line). Optional
--workers	5	Parallel workers (capped at GOMAXPROCS × 4)

# Use the embedded common JWT secrets list
jwto -j "<TOKEN>" dict

# Use a custom wordlist
jwto -j "<TOKEN>" dict --file ./wordlists/rockyou.txt --workers 10

Stops early when a match is found. Prints the secret and elapsed time on success.

sign

Tamper claims and re-sign with an HMAC secret. Supports HS256, HS384, and HS512. Verifies the secret against the original token before tampering (use --no-verify to skip).

Flag	Required	Description
--secret	Yes	HMAC signing secret
--alg	No	Signing algorithm: HS256, HS384, or HS512 (defaults to token algorithm)
--no-verify	No	Skip secret verification before signing

jwto -j "<TOKEN>" sign --secret "your-secret" -c role=admin
jwto -j "<TOKEN>" sign --secret "your-secret" --alg HS384 -r exp
jwto -j "<TOKEN>" sign --secret "your-secret" --no-verify -c role=admin

verify

Check whether an HMAC secret matches the JWT signature.

Flag	Required	Description
--secret	Yes	HMAC secret to test
--alg	No	Algorithm: HS256, HS384, or HS512 (defaults to token algorithm)

jwto -j "<TOKEN>" verify --secret "password"
jwto -j "<TOKEN>" verify --secret "password" --alg HS256

request

Send an HTTP request with custom headers. No --jwt flag needed — you control how credentials are sent (Bearer header, cookie, custom header, etc.).

Flag	Short	Required	Description
--url	-u	Yes	Target URL
--method	-X	No	GET or POST (default: GET)
--header	-H	No	Request header as Key=Value. Can be repeated
--header-file		No	File with Name: value per line. Can be repeated
--body	-d	No	Request body (POST)
--proxy		No	Proxy URL (e.g. http://127.0.0.1:8080)
--insecure	-k	No	Skip TLS certificate verification (use with intercepting proxies)
--disable-redirect		No	Do not follow HTTP redirects; return the 3xx response as-is
--headers	-I	No	Only print response headers (omit the body)

# Bearer token
jwto request -u https://api.example.com/me \
  -H "Authorization=Bearer eyJhbGci..."

# Cookie-based session
jwto request -u https://api.example.com/admin \
  -H "Cookie=session=eyJhbGci..."

# POST with body
jwto request -u https://api.example.com/login -X POST \
  -H "Authorization=Bearer eyJhbGci..." \
  -d '{"user":"admin"}'

# Headers from file (flag headers override file values)
jwto request -u https://api.example.com/api \
  --header-file ./headers.txt \
  -H "X-Custom=yes"

# Through Burp/proxy (TLS skip is opt-in)
jwto request -u https://api.example.com/me \
  -H "Authorization=Bearer eyJhbGci..." \
  --proxy http://127.0.0.1:8080 \
  --insecure

# Do not follow redirect
jwto request -u https://api.example.com/login \
  -H "Authorization=Bearer eyJhbGci..." \
  --disable-redirect

# Response headers only
jwto request -u https://api.example.com/me \
  -H "Authorization=Bearer eyJhbGci..." \
  --headers

Header file format:

Authorization: Bearer eyJhbGci...
Cookie: session=eyJhbGci...
X-Api-Key: secret

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Examples

# Inspect a token
jwto -j "<TOKEN>" debug

# None-algorithm bypass with elevated role
jwto -j "<TOKEN>" bypass -c admin=true -c role=admin

# Algorithm confusion
jwto -j "<TOKEN>" confusion --pub_key ./wordlists/public.pem

# Crack a weak HMAC secret (embedded common list)
jwto -j "<TOKEN>" dict

# Crack with a custom wordlist
jwto -j "<TOKEN>" dict --file ./wordlists/rockyou.txt

# Re-sign after tampering
jwto -j "<TOKEN>" sign --secret "password" -c admin=true

# Verify secret before signing
jwto -j "<TOKEN>" verify --secret "password"

# Send request without --jwt
jwto request -u https://api.example.com/me -H "Authorization=Bearer <TOKEN>"

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Help

jwto --help
jwto debug --help
jwto bypass --help
jwto confusion --help
jwto dict --help
jwto sign --help
jwto verify --help
jwto request --help

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Development

go test ./...
go build -o jwto ./cmd/jwto

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Disclaimer

This tool is intended for security testing and educational purposes only. Use this tool only on systems you own or have explicit permission to test. The author is not responsible for any misuse or damage caused by this program.

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Acknowledgment

• https://github.com/ticarpi/jwt_tool
• https://github.com/wallarm/jwt-secrets — source of the embedded common JWT secrets wordlist used by dict when --file is not provided