fetch_metadataFetch a web page URL and extract its title, description, Open Graph, Twitter, canonical, and JSON-LD metadata without retrieving body text.
Fetch a URL, extract title/description/OG/Twitter/canonical/JSON-LD. Not for body text.
| Name | Required | Description | Default |
|---|---|---|---|
| url | Yes | Page URL. | |
| headers | No | Headers to forward (Authorization, Cookie…). |
Changes observed during successful MCP inspections.
v0.1.1Input schema / properties / headersAdded value: +{
+ "description": "Headers to forward (Authorization, Cookie…).",
+ "type": "object"
+}Input schema / properties / url / descriptionPrevious value: -"URL to fetch (http:// or https://)."New value: +"Page URL."Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
readOnlyHint=true is consistent with a fetch operation, and the description adds useful detail by listing the exact fields returned, effectively sketching the output shape absent an output schema. It says nothing about network behavior an agent would care about: timeouts, redirect handling, non-HTML content, or failure modes on unreachable URLs.
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 action and extraction list, with the exclusion trailing. No filler whatsoever.
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 two-parameter read tool with full schema coverage and no output schema, listing the extracted fields gives the agent enough to know what comes back. The only real gap is runtime behavior on fetch failures, which is minor at this complexity level.
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 coverage is 100%, so both url and headers are already documented, including the Authorization/Cookie forwarding hint. The description adds no additional parameter semantics, so the baseline 3 applies.
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 (fetch) and resource (a URL) and enumerates exactly what is extracted: title/description/OG/Twitter/canonical/JSON-LD. The trailing 'Not for body text' sets a boundary that separates it from the body-text siblings, though no sibling is named explicitly.
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 negative case is called out directly ('Not for body text'), which is the key routing decision against fetch_extract/fetch_html/html_to_markdown. It stops short of pointing at the correct alternative by name, so the agent must infer which sibling to use for body text.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.