Decode a Base64 string back to UTF-8 text. Use for inspecting Base64-encoded API responses, JWT payload claims, config file values, or attachment data.
| Name | Required | Description | Default |
|---|---|---|---|
| input | Yes | Base64 string to decode |
| Name | Required | Description | Default |
|---|---|---|---|
| decoded | No |
Changes observed during successful MCP inspections.
Output schema / propertiesAdded value: +{
+ "decoded": {}
+}Output schema / (root)Previous value: -nullNew value: +{
+ "additionalProperties": true,
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, destructiveHint=false, and idempotentHint=true, so the safety profile is covered. The description adds that the output is UTF-8 text, clarifying that this is not binary decoding, and lists common input sources. It does not discuss error behavior on invalid Base64, but the annotation coverage lowers the burden.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
Two sentences: the first states the core action, the second gives practical use cases. No redundant wording or filler.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple single-parameter utility with robust annotations and an output schema, the description covers purpose, usage context, and output format sufficiently. No additional details are necessary.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 100% with the parameter described as 'Base64 string to decode'. The description reinforces this but does not add new semantic details beyond the schema, so a baseline score of 3 is appropriate.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description opens with 'Decode a Base64 string back to UTF-8 text', clearly stating the verb, resource, and output format. The use cases ('API responses, JWT payload claims, config file values, or attachment data') add specificity and distinguish it from sibling decode tools like decode_jwt, which targets JWT specifically.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The phrase 'Use for inspecting...' gives explicit context and typical scenarios. However, no alternatives or when-not-to-use conditions are mentioned; it doesn't explicitly compare to decode_jwt or base64_encode, so it stops short of full exclusion guidance.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.
Add one secure layer between your agents and this server.