mdl_upload_image

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

Annotations cover the safety profile (readOnlyHint=false, destructiveHint=false, idempotentHint=false), so the bar is lower, and the description adds real value beyond them: accepted formats, a 5 MiB cap on the decoded image, and the fact that the call returns a filename rather than applying anything. It does not state what happens on re-upload of the same filename or on oversize input, which is why this is a 4 rather than 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?

Three short lines, front-loaded with the operation and its limits before the per-target branching. No sentence is padding.

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 supplies the return value (upstream filename) and the downstream wiring for both targets, which is enough to call the tool correctly. Error/oversize behavior and the filename argument remain unaddressed but are peripheral.

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 must compensate: it explains both target values as distinct upload destinations and constrains image_base64 (base64, JPEG/PNG/WebP, max 5 MiB). The optional filename parameter and its pattern are left to the schema, a minor gap.

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?

Timed verb+resource ('Upload a JPEG/PNG/WebP as base64'), with format and size constraints and the return value ('upstream filename') stated up front. It also distinguishes itself from the sibling that actually applies the picture, mdl_account_map_profile_picture.

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 explicit routing per enum value: target=profile only stages the file and requires a follow-up call to mdl_account_map_profile_picture, while target=feed's returned metadata feeds a feed post. Both branches tell the agent what to do next and which alternative to reach for.

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