post_discussion_entryAdd a reply to a Canvas discussion topic by specifying the course, topic, and message. Enables direct posting from an AI agent to engage in course discussions.
Post a new entry (reply) to a discussion topic.
| Name | Required | Description | Default |
|---|---|---|---|
| message | Yes | The message body (supports HTML) | |
| topic_id | Yes | The Canvas discussion topic ID | |
| course_id | Yes | The Canvas course ID |
Changes observed during successful MCP inspections.
v1.18.11Input schema / $schemaPrevious value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"v1.18.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare openWorldHint=true and destructiveHint=true, so the description's burden is reduced, but it still adds no behavioral context. It does not clarify that the operation is additive (creating a new reply) versus destructive, nor does it mention permissions, reversibility, or side effects. The annotation destructiveHint=true is not contradicted, but the description does not elaborate on what 'destructive' might mean in this context.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
The description is a single, compact sentence that front-loads the action and resource. There is no filler or redundant phrasing. Every word contributes to the core meaning.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
The tool is a simple write operation with three required parameters fully documented in the schema. However, the description is minimal and does not explicitly state that the topic must already exist, that this is a reply operation (not creating a topic), or any expected behavior. Given the simplicity and schema coverage, it is adequate but lacks some context that would help an agent use it correctly in a workflow.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema description coverage is 100% — all three parameters (message, topic_id, course_id) are described in the schema. The description adds no additional parameter details (e.g., HTML support for message, how to find topic_id). Baseline 3 applies because the schema carries the full parameter documentation.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description states a clear action ('post') on a specific resource ('new entry (reply) to a discussion topic'). It clearly distinguishes this from sibling tools like create_discussion (which creates a new topic) and list_discussions (which reads). The verb and resource are specific and unambiguous.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
The description provides no guidance on when to use this tool versus alternatives such as create_discussion or update_discussion. It does not mention prerequisites like needing an existing topic_id, nor does it explain that this is for replying to an existing discussion rather than starting one. The usage context is only implied by the phrase 'reply to a discussion topic'.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.