Book Downloader MCP

Set active mirror

libgen_set_mirror

Pins a specific LibGen+ mirror for the session and checks it first, rejecting unreachable URLs immediately.

Instructions

Pin a specific LibGen+ mirror for this session. The mirror is probed first, so an unreachable URL is rejected immediately.

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": {
      "mirrorSrc": "<mirrorSrc>"
    },
    "name": "libgen_set_mirror"
  }
}

Input Schema

Name	Required	Description	Default
`mirrorSrc`	Yes	Base URL of a LibGen+ mirror, e.g. https://libgen.li/.

Schema Changelog

Changes observed during successful MCP inspections.

First observedv4.0.1Nov 12, 2026

TDQS

A3.8/5.0

Behavior4/5

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

Annotations already declare readOnlyHint=false, destructiveHint=false, idempotentHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely new behavior: the setting is session-scoped and the URL is probed before being accepted, so a bad mirror fails fast rather than at download time. It does not say whether a failed probe raises an error or silently keeps the previous mirror.

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?

Two short sentences, zero filler, with the scope constraint front-loaded and the validation behavior as the follow-up. Nothing could be removed without losing information.

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?

For a one-parameter, non-destructive session-state tool with no output schema, the definition covers scope and validation. The remaining gap is what the agent should expect on rejection (error shape or fallback), which matters slightly more here because the annotation marks it non-idempotent.

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 coverage is 100% and the single parameter already documents format (uri) with an example URL, so the schema carries the load. The description adds no extra constraint on the value beyond the probe behavior, which is a behavioral rather than parameter-semantic detail. 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?

"Pin a specific LibGen+ mirror for this session" gives a specific verb (pin) and resource (mirror) plus a scope qualifier (this session). It is distinguishable from libgen_list_mirrors by implication, but no sibling is named explicitly, so it stops 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 Guidelines3/5

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

The session-scoping phrasing implies the use case (override which mirror subsequent calls hit), but there is no explicit statement of when to prefer this over libgen_list_mirrors, nor any note that you should list mirrors first to obtain a valid URL. Usage is inferable rather than stated.

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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