Librus MCP Server

Message correspondents

get_message_correspondents

Read-only

List the people in a received or sent mail folder so you can filter get_messages by correspondent. Use get_recipients when addressing a new message instead.

Instructions

Modern accounts: list the people in a mailbox folder, to filter get_messages by correspondent. These references cannot address a new message; use get_recipients for that.

Input Schema

Name	Required	Description	Default
`limit`	No	Maximum items in this page.
`cursor`	No	next_cursor from the previous page; omit for the first page.
`folder`	No	received or sent mail.	received
`account_alias`	Yes	Login alias from list_accounts.

Output Schema

Name	Required	Description	Default
`items`	Yes
`identity`	Yes
`pagination`	Yes
`observation`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

Changed5 schema fields changedv2.5.0Oct 29, 2026
- removedOutput schema / $defs / CorrespondentItem / additionalProperties
```
Removed value: -false
```
- removedOutput schema / $defs / CorrespondentReferenceInput / additionalProperties
```
Removed value: -false
```
- removedOutput schema / $defs / PresentationCursor / additionalProperties
```
Removed value: -false
```
- removedOutput schema / $defs / WindowPagination / additionalProperties
```
Removed value: -false
```
- removedOutput schema / additionalProperties
```
Removed value: -false
```

Changed6 schema fields changedv2.3.1Oct 27, 2026

addedInput schema / properties / account_alias / description
```
Added value: +"Login alias from list_accounts."
```

changedInput schema / properties / account_alias / pattern

Previous value: -"^(?:[^\\s\\x00-\\x1f\\x7f]|[^\\s\\x00-\\x1f\\x7f](?:[^\\s\\x00-\\x1f\\x7f]| )*[^\\s\\x00-\\x1f\\x7f])$"New value: +"^[^\\s\\x00-\\x1f\\x7f](?: *[^\\s\\x00-\\x1f\\x7f])*$"

addedInput schema / properties / cursor / description

Added value: +"next_cursor from the previous page; omit for the first page."

addedInput schema / properties / folder / description
```
Added value: +"received or sent mail."
```
addedInput schema / properties / limit / description
```
Added value: +"Maximum items in this page."
```

changedOutput schema / $defs / CorrespondentReferenceInput / properties / account / pattern

Previous value: -"^(?:[^\\s\\x00-\\x1f\\x7f]|[^\\s\\x00-\\x1f\\x7f](?:[^\\s\\x00-\\x1f\\x7f]| )*[^\\s\\x00-\\x1f\\x7f])$"New value: +"^[^\\s\\x00-\\x1f\\x7f](?: *[^\\s\\x00-\\x1f\\x7f])*$"

First observedOct 27, 2026

TDQS

A3.9/5.0

Behavior4/5

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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely non-obvious context beyond the annotations: these correspondents cannot be used to address a new message, which prevents a predictable misuse. It says nothing about ordering or page size behavior, but those are in the schema.

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 short sentences, the primary use is front-loaded and the redirect to get_recipients follows immediately. The 'Modern accounts:' prefix uses space without conveying a clear condition to the reader.

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?

An output schema exists, so return values need no explanation, and the description correctly focuses on purpose plus the one non-obvious limitation. What remains ambiguous is the 'modern accounts' scoping, which an agent cannot resolve from any provided field.

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 limit, cursor, folder and account_alias are already documented in structured fields. The description only alludes to the folder concept ('in a mailbox folder') and adds no format or constraint detail beyond the schema. 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 and resource: 'list the people in a mailbox folder'. It also ties the output to a downstream use (filtering get_messages by correspondent). The leading 'Modern accounts:' qualifier is unexplained and slightly clouds what the tool actually returns.

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?

Gives an explicit positive use case (filter get_messages by correspondent) and an explicit anti-use case with the correct alternative (use get_recipients to address a new message). No guidance on pagination or which folder to choose, but the schema covers those fields.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.