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

The description discloses important behavior beyond annotations: 'full-array write; empty array clears' and 'Immediate write — the tag chips appear on the activity card.' It also explains the semantic implications of each tag. Annotations only state readOnlyHint=false, destructiveHint=false, so the description adds meaningful operational detail without contradicting 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?

The description is long, but it is front-loaded with the core behavior and then structured as a compact list of tag definitions. Each tag explanation earns its place because it directly affects how the agent should tag and interpret activities. It could be slightly more concise, but there is no fluff.

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 tool with no output schema and minimal annotations, the description is exceptionally complete. It covers purpose, usage triggers, write behavior, parameter semantics, and all enum values with domain-specific interpretation guidance. An agent has enough information to invoke the tool correctly without needing additional context.

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 full responsibility for parameter meaning. It thoroughly explains the tags array semantics, including full-array overwrite and empty-array clearing, and gives detailed meaning for every enum value. The id parameter is not explicitly described, but it is clearly implied by 'one completed activity' and the overall context.

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?

The description opens with a specific verb and resource: 'Set CONTEXT tags on one completed activity'. It also explains the full-array write semantics and explicitly distinguishes tags as describing how the session should be read, not what it contained. This clearly separates the tool from siblings like set_activity_notes or edit_activity.

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 gives explicit usage triggers: 'Use when the athlete tells you the context... or when you infer it and they confirm.' It also provides example phrases the athlete might use. It does not name alternative tools for exclusion, but the guidance is concrete enough for an agent to decide when to invoke it.

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