Look up the MIME type for a file extension, or the usual extensions for a MIME type. Pure CPU, instant.
Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.
{
"id": 1,
"jsonrpc": "2.0",
"method": "tools/call",
"params": {
"arguments": {
"q": "<q>"
},
"name": "mime_lookup"
}
}| Name | Required | Description | Default |
|---|---|---|---|
| q | Yes | Extension or MIME type |
Changes observed during successful MCP inspections.
Input schema / properties / qAdded value: +{
+ "description": "Extension or MIME type",
+ "type": "string"
+}Input schema / requiredAdded value: +[
+ "q"
+]Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description must carry the behavioral burden. 'Pure CPU, instant' usefully discloses that this is a fast local operation with no side effects, but it omits whether unknown values return errors or empty results and does not describe the return shape.
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 short sentences, front-loaded with the core action and scope. No wasted wording.
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 one-parameter, non-mutating lookup tool with no output schema, the description gives enough context to invoke it correctly. Minor gaps around return format and unknown-input behavior remain, but they are small relative to the tool's simplicity.
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 description coverage is 100%, so the baseline is 3. The description restates that 'q' can be either a file extension or a MIME type, but adds no format examples or constraints beyond the schema.
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 states a specific verb ('look up') and resource ('MIME type' / 'extensions') and makes the bidirectional behavior clear. However, it does not distinguish itself from the sibling tool 'mime_types', so an agent cannot tell from this description alone whether they overlap.
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?
It implies when to use the tool by describing both lookup directions: extension-to-MIME and MIME-to-extension. It does not state exclusions, alternatives, or what happens for unknown inputs.
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.