canvas_module_file

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

Annotations already declare read-only, idempotent, open-world, non-destructive behavior, and the description adds real value on top: a 15 MiB maximum, the fact that it returns an MCP file resource for host materialization rather than inline text, and the caveat that the host may not expose it as an attachment. It does not describe failure behavior for unsupported item types or how ExternalUrl resolution works, keeping it from a 5.

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 critical scope and return-type information is front-loaded in the first two sentences, and each sentence carries operational content. The closing caution about not claiming attachment is slightly redundant with the 'host to materialize as an attachment' clause, but it prevents a concrete failure mode.

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?

With no output schema, the description correctly compensates by explaining what is returned (an MCP file resource) and its size ceiling. For a simple 3-ID retrieval tool this is nearly complete; only error/edge-case behavior for non-file module item types is unaddressed.

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 coverage is 100%, so the three Canvas ID parameters are already fully documented in the schema, including their provenance (canvas_module_items, canvas_courses, canvas_modules). The description adds only the ID-vs-URL constraint, which the integer types already imply, 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 and resource ('Retrieve the ORIGINAL binary file attached to an accessible Canvas module item') and narrows scope to File/ExternalUrl items including Dropbox shared PDFs. It also implicitly separates itself from text-extraction siblings by saying it returns a file resource, 'not extracted text'.

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?

Gives concrete usage context: 'Only accepts Canvas IDs, never a URL' and 'Use the returned file for page-by-page reading', plus a caution about not claiming attachment. It stops short of naming a sibling alternative (e.g., the content/text variant) explicitly, so the when-to-use-this-vs-that routing is implied rather than spelled out.

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