MCPFax Feed Reader

Find the feed for a website

discover_feeds

Given a site's normal URL, return the feeds it declares in its HTML head, each with title and type. Use when you know a site publishes updates but not where its feed lives. If the page declares none, conventional locations are suggested and clearly marked as guesses that may 404. Costs $0.005 USDC per call via x402 on Base.

Tool call template

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": "discover_feeds"
  }
}

Input Schema

Name	Required	Description	Default
`url`	Yes	The site's page URL, e.g. 'https://blog.rust-lang.org'.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 4, 2026
- addedInput schema / properties / url / examples
```
Added value: +[
+  "https://blog.rust-lang.org"
+]
```
First observedSep 1, 2026

TDQS

A4.5/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

With no annotations provided, the description carries the full burden of behavioral disclosure. It explains the return shape, the fallback behavior of suggesting conventional locations marked as guesses that may 404, and discloses the cost of $0.005 USDC per call via x402 on Base. This is unusually transparent.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is compact and front-loaded, leading with the core behavior, then the use case, fallback behavior, and cost. Every sentence earns its place and there is no redundant or filler wording.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool is simple with one parameter and no output schema, and the description covers the return value, the use case, the failure/fallback case, and cost. An agent has enough information to invoke the tool correctly and interpret results.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The input schema already describes the single url parameter fully with an example and explanation, so schema coverage is 100%. The description adds only the phrase 'normal URL,' which is mildly clarifying but does not substantially go beyond the schema.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a specific verb and resource: given a site's normal URL, return the feeds it declares in its HTML head, each with title and type. This clearly distinguishes the tool from siblings like read_feed, which likely fetch and parse feed content rather than discovering feed locations.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description explicitly states when to use the tool: when you know a site publishes updates but not where its feed lives. It does not explicitly name alternatives or state when not to use it, but the use case is clear enough for an agent to select it appropriately.

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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