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cyber-chef-mcp

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cyberchef_from_base64

Decode Base64 strings into readable UTF-8 text, including URL-safe variants. Strips whitespace and handles padding automatically.

Instructions

Decodes standard RFC 4648 or URL-safe Base64 encoded strings into readable UTF-8 plaintext. Automatically strips whitespace and handles padding.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
inputYesThe Base64 encoded string to decode (e.g., 'SGVsbG8gV29ybGQ=').
urlSafeNoOptional boolean. Set to true if the input uses URL-safe Base64 encoding with '-' and '_' instead of '+' and '/'.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed2 schema fields changedv1.0.2
    • changedInput schema / properties / input / description
      Previous value: -"Base64 string to decode"New value: +"The Base64 encoded string to decode (e.g., 'SGVsbG8gV29ybGQ=')."
    • changedInput schema / properties / urlSafe / description
      Previous value: -"Set true if URL-safe Base64 (- and _ characters)"New value: +"Optional boolean. Set to true if the input uses URL-safe Base64 encoding with '-' and '_' instead of '+' and '/'."
  2. First observedv1.0.1

TDQS

A4/5.0
Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It goes beyond the bare purpose by noting that whitespace is automatically stripped and padding is handled, which are useful non-obvious behaviors. It does not describe failure on invalid Base64 input, but the stated behavior is otherwise clear and honest.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is two sentences with no filler, and the primary action is front-loaded in the first word. Every clause adds useful information about behavior or output.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a simple two-parameter decoder, the description is largely complete: it explains the input format, supported variants, output type, and two edge-case behaviors. It could mention invalid-input handling, but that is a minor omission given the tool's simplicity and the schema's thorough parameter documentation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already fully documents both the input and urlSafe parameters. The tool description does not add meaning beyond the schema, matching the baseline expectation for high schema coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description opens with a specific verb and resource: 'Decodes standard RFC 4648 or URL-safe Base64 encoded strings into readable UTF-8 plaintext.' It clearly states the tool's function and distinguishes it from siblings like cyberchef_to_base64 and cyberchef_from_hex.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies the tool should be used when a user has Base64-encoded text and wants readable plaintext, but it does not explicitly say when to prefer it over alternatives such as cyberchef_magic or cyberchef_url_decode. It also does not mention the urlSafe parameter's role in switching behavior, leaving that to the schema.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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