mcp-server-mattermost

pin_message

Idempotent

Pin a message in a Mattermost channel to highlight it in the pinned posts section for easy reference.

Instructions

Pin a message in a channel.

Pinned messages appear in the channel's pinned posts section. Pinning an already pinned message has no additional effect.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`post_id`	Yes	26-character post/message identifier (e.g., 'o5w8h47pdfbzjc4d8w7dhnhren')

Output Schema

TableJSON Schema

Name	Required	Description
`id`	Yes	Unique post identifier
`type`	Yes	Post type (empty for regular posts)
`edit_at`	Yes	Last edit timestamp
`message`	Yes	Post content (supports Markdown)
`root_id`	Yes	Root post ID if in thread
`user_id`	Yes	Author user identifier
`file_ids`	No	Attached file IDs
`hashtags`	Yes	Space-separated hashtags
`create_at`	Yes	Creation timestamp in milliseconds
`delete_at`	Yes	Deletion timestamp (0 if not deleted)
`is_pinned`	Yes	Whether post is pinned
`update_at`	Yes	Last update timestamp in milliseconds
`channel_id`	Yes	Channel where posted
`original_id`	Yes	Original post ID if edited
`pending_post_id`	Yes	Client-side pending ID

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedv0.6.1Sep 10, 2026

changedOutput schema / required

Previous value: -[
-  "id",
-  "create_at",
-  "update_at",
-  "delete_at",
-  "edit_at",
-  "user_id",
-  "channel_id",
-  "root_id",
-  "original_id",
-  "message",
-  "type",
-  "hashtags",
-  "file_ids",
-  "pending_post_id",
-  "is_pinned"
-]New value: +[
+  "id",
+  "create_at",
+  "update_at",
+  "delete_at",
+  "edit_at",
+  "user_id",
+  "channel_id",
+  "root_id",
+  "original_id",
+  "message",
+  "type",
+  "hashtags",
+  "pending_post_id",
+  "is_pinned"
+]

First observedv0.5.1Jul 29, 2026

TDQS

A4.1/5.0

Behavior4/5

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

The annotations already provide idempotentHint=true and destructiveHint=false, and the description adds meaningful behavioral context: it states the observable effect (message appears in pinned posts) and explicitly clarifies the idempotent behavior ('Pinning an already pinned message has no additional effect'). This goes beyond simply restating the annotation booleans. No contradiction with annotations is present.

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 three short sentences, each with a distinct purpose: state the action, describe the result, and clarify the idempotent edge case. There is no filler or repetition of schema details. It is front-loaded and compact.

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?

For a simple one-parameter mutating operation, the description plus annotations and schema cover everything an agent needs: required identifier, effect, idempotence, and non-destructive nature. An output schema exists, so return-value documentation is not required here. No meaningful gap remains.

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 only parameter, post_id, is already well-documented with type and example. The description adds no extra meaning about the parameter itself, but it also does not need to, since the schema carries the full burden. Baseline 3 is appropriate.

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 opens with a specific verb and resource: 'Pin a message in a channel.' It clearly defines the tool's function and distinguishes it from the sibling 'unpin_message' by direction of action. Even without reading the schema, an agent knows exactly what this operation does.

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 description implies usage context by explaining that pinned messages appear in the channel's pinned posts section and that pinning an already pinned message is a no-op. However, it does not explicitly state when to prefer this over alternatives or when not to use it. Usage guidance is adequate but mostly inferred rather than stated.

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