Source: https://guthlabs.ai/docs/instruments/base64-url-encoding-converter/implementation/

instrument implementation / implementation-contract

# Base64 / URL Encoding Converter implementation

A source-bound implementation contract for Base64 / URL Encoding Converter; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t4-255

**Effect**: Computation or source lookup only

## Input and validation requirements

Malformed Base64 input of length 1 has no defined decode result and must be rejected. URL encoding also has a genuine convention hazard: RFC 3986 produces %20 for spaces, while form-style encoding produces '+'.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "inputs": {
    "direction": "encode",
    "mode": "base64",
    "text": "Hello",
    "text_encoding": "UTF-8"
  },
  "expected_outputs": {
    "converted_string": "SGVsbG8=",
    "byte_size_before": 5,
    "byte_size_after": 8
  },
  "working": "UTF-8 bytes for “Hello”: H=1, e=1, l=1, l=1, o=1, so 5 bytes. Base64 groups: ceil(5/3)=2 groups. Output size = 2×4 = 8 characters/ASCII bytes. The first 3 bytes encode to “SGVs”; the remaining 2 bytes encode to “bG8=” with one '=' padding character. Result: “SGVsbG8=”."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/base64-url-encoding-converter/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/base64-url-encoding-converter/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/base64-url-encoding-converter/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche4/tranche4-results.json`