lookup_mimeGet the MIME (media) type for a filename or extension, e.g. "photo.png" or "png" -> "image/png". Keyless, offline.
| Name | Required | Description | Default |
|---|---|---|---|
| file | Yes | A filename or bare extension, e.g. "report.pdf" or "pdf". |
Changes observed during successful MCP inspections.
Input schema / examplesAdded value: +[
+ {
+ "file": "document.pdf"
+ },
+ {
+ "file": "png"
+ }
+]Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true, destructiveHint=false, etc., covering behavioral safety. The description adds value by noting 'Keyless, offline' and providing an output example. It does not mention error handling for invalid inputs, but overall transparency is good.
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?
The description is extremely concise: one sentence with an example and a short note 'Keyless, offline.' No wasted words; every part earns its place.
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?
Given no output schema, the description provides an output example ('image/png'), which is sufficient. Annotations cover safety, and the parameter is fully documented. The tool is simple and the description is complete for its complexity.
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%, with the parameter 'file' well-described. The description adds context by showing the output format and confirming offline operation, which goes beyond the schema. The baseline of 3 is exceeded because of added value.
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 clearly states the tool's purpose: to get the MIME type for a filename or extension, with a concrete example. It uses a specific verb (get) and resource (MIME type), and the purpose is distinct from all sibling tools, which are unrelated.
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 description mentions 'Keyless, offline' which gives context on when to use (no API key needed, offline), but it does not provide explicit guidance on when not to use or mention alternatives. Given the tool's simplicity, the implied usage is clear, but lacking explicit when-not-to-use prevents a higher score.
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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