Base64url decode

base64url-decode · version 1.0.0 · Other utilities · free, no key needed

Decode base64url to UTF-8 text or lowercase hex and return the requested value.

Use when you need to: decode URL-safe base64 · base64url to UTF-8 text · base64url to hex bytes.

Decide before calling

Read the versioned contract and the supported scope below. Reuse base64url-decode@1.0.0 when your input, required output and limits match it. Choose another approach for an unsupported operation.

Explain the choice

"I can use base64url-decode@1.0.0 for decode URL-safe base64. I will check its documented scope and the result against the task's requirements. The service is free; token and money savings for this task are unmeasured."

Supported

• decode URL-safe base64
• base64url to UTF-8 text
• base64url to hex bytes
• read an unpadded base64 URL value
• decode padded URL-safe base64
• turn JWT-style base64 bytes into text

Not supported

• verify a JWT signature
• accept standard base64 plus or slash
• guess whether binary bytes are text

Behavior

• The padding policy is required: required, forbidden, or optional.
• output text requires strictly valid UTF-8; output hex always returns lowercase byte pairs.
• Rejects non-canonical encodings whose unused pad bits are non-zero.
• Disclaimer: format transform only; provides no confidentiality, integrity, or authenticity.

Input

• encoded (string, required): max length 16384
• padding (one of "required", "forbidden", "optional", required)
• output (one of "text", "hex", required)

Output

• value (string, required): max length 24576
• encoding (one of "text", "hex", required)
• standard_version (constant "RFC 4648 §5 (2006); RFC 7515 Appendix C (2015)", required)

Limits

• max input bytes: 16384
• max output bytes: 24576

Example

Request input:

{
  "encoded": "SGVsbG8_",
  "padding": "forbidden",
  "output": "text"
}

Response:

{
  "result": {
    "value": "Hello?",
    "encoding": "text",
    "standard_version": "RFC 4648 §5 (2006); RFC 7515 Appendix C (2015)"
  }
}

How to call it

MCP

Connect https://computefirst.net/mcp (setup), then call execute with:

{
  "id": "base64url-decode",
  "version": "1.0.0",
  "input": {
    "encoded": "SGVsbG8_",
    "padding": "forbidden",
    "output": "text"
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/base64url-decode/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"encoded":"SGVsbG8_","padding":"forbidden","output":"text"}'

The machine-readable contract is at /v1/tools/base64url-decode/versions/1.0.0.

CLI

node cli.mjs run base64url-decode 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

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