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

Annotations declare the write/openWorld/destructive profile, and the description adds real behavioral context beyond them: the multipart upload shape, the exact `/upload-service/upload` path, and the absence of extension suffix and import headers. It doesn't state permission requirements or failure behavior, but the added mechanics are useful.

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?

Purpose is front-loaded, but the sentence is dense and partly circular, restating the device-sync idea twice ('plain device-sync upload path' and 'ordinary device-sync-shaped upload') and piling on jargon like 'load-bearing import headers' and 'spoofed-client'.

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 an upload tool with no output schema, the description covers the routing, path, and encoding-relevant context, and the schema handles the inputs. It is complete enough to invoke correctly, though it omits return/confirmation behavior.

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%, with all three parameters (content, encoding, filename) fully documented including format guidance for .fit/.gpx/.tcx. The description adds no parameter-level meaning beyond the schema, so the 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 (uploads) and resource (activity file) and immediately distinguishes itself from the sibling import_activity by contrasting the plain device-sync path with the spoofed-client import. An agent can tell these two apart without opening either schema.

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?

Names the alternative sibling (importActivity) and characterizes the difference (plain device-sync vs import headers/spoofed client), giving clear context for selecting this tool. It stops short of an explicit 'use this when X, use import_activity when Y' decision rule, leaving some inference to the agent.

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