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Canvas LMS MCP Server

Canvas LMS MCP Server

by bruchris
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Hybrid

Post Discussion Entry

post_discussion_entry
Destructive

Post a new entry (reply) to a discussion topic in a course, and return the created entry (id, user_id, message, created_at). Not idempotent: each call adds another reply, Canvas does not deduplicate repeated calls.

Instructions

Post a new entry (reply) to a discussion topic in a course, and return the created entry (id, user_id, message, created_at). Not idempotent: each call adds another reply, Canvas does not deduplicate repeated calls. Works even on a topic Canvas has made anonymous, where get_discussion itself 404s — use list_discussions to confirm the topic exists and find its topic_id. Requires the caller to have an active enrollment in the course with permission to post to the forum, which Canvas grants to students, TAs and instructors by default unless an admin has restricted it.

Input Schema

NameRequiredDescriptionDefault
messageYesThe message body (supports HTML)
topic_idYesThe Canvas discussion topic ID
course_idYesThe Canvas course ID

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed4 schema fields changedv1.18.15
    • addedInput schema / properties / course_id / anyOf
      Added value: +[
+  {
+    "exclusiveMinimum": 0,
+    "maximum": 9007199254740991,
+    "type": "integer"
+  },
+  {
+    "pattern": "^[1-9][0-9]{0,18}$",
+    "type": "string"
+  }
+]
    • removedInput schema / properties / course_id / type
      Removed value: -"number"
    • addedInput schema / properties / topic_id / anyOf
      Added value: +[
+  {
+    "exclusiveMinimum": 0,
+    "maximum": 9007199254740991,
+    "type": "integer"
+  },
+  {
+    "pattern": "^[1-9][0-9]{0,18}$",
+    "type": "string"
+  }
+]
    • removedInput schema / properties / topic_id / type
      Removed value: -"number"
  2. Changed1 schema field changedv1.18.11
    • changedInput schema / $schema
      Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"
  3. First observedv1.18.0

TDQS

A4.9/5.0
Behavior5/5

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

Beyond the destructiveHint and openWorldHint annotations, the description discloses critical behavior: repeated calls are not deduplicated, each call creates another reply, anonymous topics behave differently from get_discussion, and posting depends on enrollment and forum permissions. These are exactly the side effects and constraints an agent needs before calling a mutating endpoint.

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 purpose and return value are front-loaded in the first sentence, followed by non-idempotency, anonymous-topic handling, and permission requirements. Every sentence adds operational value, and the description avoids redundant repetition.

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?

The tool is a mutating discussion operation with no output schema, but the description covers the return shape, non-idempotent side effects, anonymous-topic edge cases, and authorization requirements. Given the annotations and full schema coverage, this is complete enough for correct invocation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all three parameters are already documented in the schema. The description adds useful semantic context for topic_id by explaining how to find it via list_discussions, especially for anonymous topics. It does not add further detail for course_id or message beyond the schema, so it is slightly above the baseline rather than a full 5.

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: post a new entry (reply) to a discussion topic in a course. It also clarifies that it returns the created entry, distinguishing it from topic-creation and general discussion-reading tools. The scope is precise enough for an agent to identify the correct action without opening sibling schemas.

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

Usage Guidelines5/5

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

The description gives explicit usage context: use list_discussions to confirm topic existence and find topic_id, especially because get_discussion 404s on anonymous topics. It also warns that the operation is non-idempotent and that each call adds another reply, which directly guides safe invocation behavior.

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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