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.
Input schema / examplesAdded value: +[
+ {
+ "input": "aMOpbGxvIPCfjI0="
+ }
+]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 readOnly, idempotent, non-destructive, closed-world behavior, so safety is covered. The description adds the meaningful behavioral detail that the output is UTF-8 text, which tells the agent how to interpret the result; it stops short of stating what happens with invalid Base64 or non-UTF-8 binary bytes.
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, front-loaded with what the tool does and followed by when to use it. Every clause earns its place with no restating of the name or redundant framing.
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?
With an output schema handling return values, rich annotations handling the safety profile, and a fully documented single parameter, the description covers nearly everything needed to invoke it correctly. The remaining minor gap is error behavior on invalid or non-UTF-8 input, which neither the description nor the visible schema addresses.
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?
There is a single required parameter with 100% schema description coverage, so the schema already carries parameter semantics. The description restates only that it is a Base64 string and adds no format or validation guidance beyond the schema — baseline 3.
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?
States a specific verb and resource ('Decode a Base64 string') plus the exact output interpretation ('back to UTF-8 text'), making the operation unambiguous. The verb contrast with base64_encode and the explicit UTF-8 output type let an agent distinguish it from encode and from text-formatting siblings without opening the schema.
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 second sentence gives concrete usage contexts (API responses, JWT payload claims, config values, attachment data), which is clear guidance on when to reach for this tool. It does not name an alternative or exclusion — notably it overlaps with the decode_jwt sibling for JWT payloads without routing the agent between them.
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.