Fetch Open Graph / meta metadata for a public URL. Costs $0.01 USDC on Base.
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": {
"url": "<url>"
},
"name": "preview_url"
}
}| Name | Required | Description | Default |
|---|---|---|---|
| url | Yes |
Changes observed during successful MCP inspections.
Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the burden of disclosure. It reveals the economic cost and the public-access requirement, and implies a read-only network fetch. It does not detail failure modes or payment flow, but these are not critical for a simple fetch operation.
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 with no filler. The primary action is front-loaded, and the critical cost detail is included in the second sentence.
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 tool with no siblings or output schema, the description covers purpose, access constraint, and cost. The return structure is only loosely implied, but 'Open Graph / meta metadata' gives a reasonable expectation.
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?
The schema only provides an unnamed 'url' string with no description. The description compensates by defining the URL as public and as the target for metadata extraction, adding meaningful semantics 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 uses a specific verb ('Fetch'), names the resource ('Open Graph / meta metadata'), and adds a clear scope ('for a public URL'). Even without siblings, an agent knows exactly what the tool does.
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 clearly states the tool is intended for public URLs, which serves as an eligibility constraint. It also surfaces the cost, which is essential usage information. No alternatives are mentioned, but none exist in the provided context.
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.