post_discussion_entryPost a new entry (reply) to a discussion topic.
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.
v1.18.15Input schema / properties / course_id / anyOfAdded value: +[
+ {
+ "exclusiveMinimum": 0,
+ "maximum": 9007199254740991,
+ "type": "integer"
+ },
+ {
+ "pattern": "^[1-9][0-9]{0,18}$",
+ "type": "string"
+ }
+]Input schema / properties / course_id / typeRemoved value: -"number"Input schema / properties / topic_id / anyOfAdded value: +[
+ {
+ "exclusiveMinimum": 0,
+ "maximum": 9007199254740991,
+ "type": "integer"
+ },
+ {
+ "pattern": "^[1-9][0-9]{0,18}$",
+ "type": "string"
+ }
+]Input schema / properties / topic_id / typeRemoved value: -"number"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 already declare openWorldHint=true and destructiveHint=true, which is surprising for a reply-post and warrants explanation the description never provides. The description adds no behavioral context such as whether the post is visible immediately, whether it requires enrollment, or what the destructiveHint refers to. It does not contradict the annotations, but it adds nothing beyond them.
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?
A single front-loaded sentence with no filler or redundancy. It is appropriately sized for a simple mutation, though it stops short of carrying any routing or behavioral payload.
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?
For a three-parameter, fully-required mutation with no output schema and annotations covering the safety profile, the description is minimally viable. However, the odd destructiveHint and the posting-permission context are left unexplained, so it is adequate rather than complete.
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%, so all three required parameters (course_id, topic_id, message) are already documented, including the HTML support note for message. The description repeats none of this and adds no syntax or format detail, so baseline 3 applies.
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?
States a specific verb (Post) and resource (a new entry/reply to a discussion topic), which cleanly distinguishes it from the sibling topic-level tools like create_discussion and update_discussion. It does not explicitly name those siblings, so the differentiation is inferred rather than stated.
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 offers no when-to-use guidance, no prerequisites (e.g., enrollment or course permissions), and no alternatives. The only implied usage comes from the purpose statement itself; there is no explicit routing to or away from any sibling.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.