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cyber-chef-mcp

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cyberchef_from_base64

Decode standard or URL-safe Base64 strings into UTF-8, hex, printability, and byte length, separating readable text from binary secrets without mojibake corruption.

Instructions

Decodes RFC 4648 standard or URL-safe Base64 encoded strings and returns structured output { utf8, hex, isPrintable, byteLength }. Crucial: Distinguishes printable text from raw binary ciphertext/TOTP secrets without mojibake data corruption.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
inputYesThe Base64 encoded string to decode (e.g., 'SGVsbG8gV29ybGQ=').
urlSafeNoOptional boolean. Set to true if input uses URL-safe Base64 ('-' and '_' without padding).

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.0.4
    • changedInput schema / properties / urlSafe / description
      Previous value: -"Optional boolean. Set to true if the input uses URL-safe Base64 encoding with '-' and '_' instead of '+' and '/'."New value: +"Optional boolean. Set to true if input uses URL-safe Base64 ('-' and '_' without padding)."
  2. 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 '/'."
  3. First observedv1.0.1

TDQS

A3.9/5.0
Behavior4/5

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

No annotations exist, so the description carries the full burden, and it does disclose the return structure { utf8, hex, isPrintable, byteLength } and the no-mojibake behavior for non-printable input. It stops short of describing error handling on malformed or unpadded Base64 input, which is the main remaining behavioral gap.

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

Conciseness4/5

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

Two sentences with no wasted words, and the core decode purpose plus output shape are front-loaded. The 'Crucial:' framing is slightly promotional, but the content it introduces is substantive.

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 2-parameter decode tool with no output schema, the description usefully enumerates the returned fields and covers the URL-safe variant. Only invalid-input behavior is left unaddressed, which is a minor gap at this complexity.

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 coverage is 100%, so the schema already documents both 'input' with an example and 'urlSafe' with its meaning. The description's mention of 'URL-safe Base64' only loosely signals the urlSafe flag and adds no syntax or format detail beyond the schema, so the baseline 3 applies.

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?

States a specific verb (Decodes) and resource (RFC 4648 standard or URL-safe Base64 strings) and even names the return shape. The 'from' vs the sibling cyberchef_to_base64's 'to' direction is unambiguous, so an agent can pick it without opening either schema.

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?

Usage is implied by the decode verb, and the 'Crucial' clause hints at relevant scenarios (binary ciphertext, TOTP secrets) where raw-byte handling matters. However, it never states when to prefer this over cyberchef_from_hex, cyberchef_magic, or the other decode siblings, and gives no prerequisites or exclusions.

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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