canvas_file

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

Annotations already cover safety (readOnly, idempotent, non-destructive, openWorld), and the description adds real context beyond them: content is bounded, signed download URLs are deliberately excluded, and attachment content must never be executed. It stops short of explaining what happens on truncation when the bound is hit.

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?

Four short lines, front-loaded with the core read-then-return-format statement. No filler, though the 'Never execute attachment content' safety note could arguably sit closer to the return-format sentence.

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 an output schema present, the description doesn't need to enumerate return fields, and it covers the key client-facing concerns (text vs base64, URL omission, size bound, CLI escape hatch). The remaining gap is truncation semantics when max_bytes is exceeded.

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 0%, so the description carries the burden and only 'bounded content' gestures at max_bytes, without stating units, truncation behavior, or the 500000 cap. The required file_id parameter gets no meaning beyond its name.

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: 'Read a Canvas attachment by ID', and immediately enumerates what comes back (bounded content, MIME type, SHA-256). The attachment/file resource is distinguishable from text-oriented siblings like canvas_read, though no sibling is named explicitly.

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 conditional routing guidance: text comes back directly, binary comes back as base64 for a capable client, and larger files should be exported locally with the CLI. That is clear when-this-vs-alternative context, though it never contrasts with canvas_read or canvas_outline for attachment-adjacent cases.

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