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substack-mcp

substack-mcp

by andersschaffner
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
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get_post_by_url

Retrieve a full Substack post by its URL to fetch content, metadata, and citations for research, archiving, or reference.

Instructions

Retrieve a specific post by its URL

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": "get_post_by_url"
  }
}

Input Schema

NameRequiredDescriptionDefault
urlYesFull URL of the Substack post

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv1.0.0

TDQS

C2.9/5.0
Behavior2/5

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

No annotations are provided, so the description carries the full behavioral burden, and it discloses almost nothing. It does not say what happens on an invalid/unresolvable URL, whether auth is required, or what is returned. The only implicit signal is that it is a read operation.

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

Conciseness4/5

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

A single efficient sentence with no filler, and the identifying detail (by its URL) is front-loaded. It is under-specified rather than verbose, which is a content problem rather than a structure problem.

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

Completeness3/5

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

For a one-parameter read tool with full schema coverage and no output schema, the description is just barely sufficient. It omits any return-shape or failure-mode context, which leaves an agent guessing about error handling.

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?

Schema description coverage is 100% and the single url parameter is already documented as the full URL of the Substack post. The description adds no format details (e.g. slug or canonical form requirements) beyond the schema, so the baseline 3 applies.

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

Purpose4/5

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

States a specific verb (Retrieve) and resource (a specific post) plus the lookup key (URL), which implicitly separates it from the sibling get_post_by_title. No explicit sibling naming, so it falls short of a 5.

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

Usage Guidelines2/5

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

No when-to-use guidance at all: it never says when a URL lookup is preferable to search_posts or get_post_by_title, nor does it mention prerequisites such as requiring the post to be public. The agent must infer all routing from the tool name.

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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