Narrareach

List creator matches

list_creator_matches

Read-onlyIdempotent

List Substack’s creator matches for a publication: other writers whose audience overlaps, with their public profile, subscriber label, overlap counts, and whether this publication already messaged them. Read-only; it never sends a message. Workspace owner only, on a plan that includes agents.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "list_creator_matches"
  }
}

Input Schema

Name	Required	Description	Default
`workspace`	No	Optional authorized team workspace name or id. Absence selects the authenticated user’s personal account. Audience is for the workspace owner only.
`publicationId`	No	Optional connected Substack publication: its id, handle, URL, or name. Defaults to the default publication, or the only one.

Output Schema

Name	Required	Description	Default
`matches`	Yes
`publicationId`	Yes
`connectedAccount`	No

Schema Changelog

Changes observed during successful MCP inspections.

AddedOct 18, 2026

TDQS

A3.9/5.0

Behavior4/5

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

Annotations already declare readOnly, idempotent and non-destructive, so the bar is lower; the description still adds real context by asserting it 'never sends a message' and by stating the owner-only and plan-gating constraints. It does not cover pagination or result limits, keeping it short of a 5.

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?

Two sentences, front-loaded with the core purpose, and the trailing clause about read-only behavior is short and earns its place. Slightly dense with enumerated fields but no wasted text.

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

Completeness4/5

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

With an output schema present, return values need not be explained, and annotations cover the safety profile; the description supplies permission and plan prerequisites plus the overlap semantics. Only the lack of pagination/volume guidance and any sibling prioritization keeps it from a 5.

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%, so the workspace and publicationId semantics are already fully documented in the schema, and the description adds no format or defaulting detail beyond it. Baseline 3 applies.

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 ('List Substack's creator matches for a publication') and defines what a match actually is ('other writers whose audience overlaps'), plus enumerates the returned fields. That scope is distinct from siblings like list_notes or list_social_accounts, so an agent can route correctly without opening the schema.

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

Usage Guidelines3/5

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

It supplies prerequisites ('Workspace owner only, on a plan that includes agents') but never says when to prefer this over alternatives such as get_audience_overview or preview_audience_segment. Usage is implied by the resource name rather than contrasted with neighbors.

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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