I used the same url for two different postings.
Captures rendered webpage screenshot image data ($0.01 USDC)
| Name | Required | Description | Default |
|---|---|---|---|
| url | Yes | Target website URL to render and capture |
| Name | Required | Description | Default |
|---|---|---|---|
| title | No | Page title | |
| success | Yes | Capture status | |
| screenshotBase64 | No | Base64 encoded PNG screenshot |
Changes observed during successful MCP inspections.
Input schema / properties / url / descriptionAdded value: +"Target website URL to render and capture"Output schema / (root)Previous value: -nullNew value: +{
+ "properties": {
+ "screenshotBase64": {
+ "description": "Base64 encoded PNG screenshot",
+ "type": "string"
+ },
+ "success": {
+ "description": "Capture status",
+ "type": "boolean"
+ },
+ "title": {
+ "description": "Page title",
+ "type": "string"
+ }
+ },
+ "required": [
+ "success"
+ ],
+ "type": "object"
+}Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare the tool read-only and open-world, so the description is not required to repeat that. It adds meaningful behavioral context by disclosing the $0.01 USDC cost and the fact that the result is rendered image data rather than raw HTML or text. There is no contradiction with annotations.
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 a single efficient sentence that front-loads the core action and includes the cost detail without any filler. Every part contributes information value.
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 one-parameter tool, the description plus annotations and output schema provide sufficient context. The only minor gap is explicit guidance about when to use this over the scraping siblings, but the core calling information is complete.
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 single parameter is fully documented in the schema ('Target website URL to render and capture'), and schema description coverage is 100%. The description does not add extra meaning beyond 'webpage', so the baseline 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 uses a specific verb and resource: it captures 'rendered webpage screenshot image data'. This clearly differentiates the tool from text-oriented siblings like web_scraper, browser_scraper, and pdf_extractor, and the cost hint adds a useful distinguishing detail.
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 implies the tool is for obtaining a visual screenshot of a webpage, but it does not explicitly state when to prefer it over browser_scraper or web_scraper, and it gives no exclusions or prerequisites. The usage context is clear but only by inference.
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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