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

Annotations already include idempotentHint=true, destructiveHint=true, and readOnlyHint=false, so the safety profile is established. The description adds useful context by emphasizing that repeated calls are acceptable, but it does not disclose side effects like clearing fields via null or the destructive overwrite nature beyond what the schema and annotations already imply.

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 a single, compact sentence that front-loads the core action and includes actionable usage guidance. Every clause earns its place, and there is no redundant filler.

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 simple three-parameter tool with a complete schema, rich annotations, and an output schema, the description is nearly sufficient. It clearly communicates the identity-matching behavior and idempotency; the only gap is not explicitly routing multi-record scenarios to the bulk sibling.

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%, so every parameter is already documented in the input schema. The description does not need to restate parameter details; it adds only the 'by externalId' matching hint, which is also present in the schema's externalId description. This is the baseline where the schema carries the weight.

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 clearly states the action ('Upserts a learner by externalId') and the resource, so an agent knows exactly what the tool does. It does not explicitly name or contrast with sibling tools like bulk_upsert_identities, but the singular 'a learner' and 'by externalId' communicate the core scope.

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 concrete guidance on when to use the tool: 'call this every time you know who the learner is, as often as you like.' It conveys idempotency and frequent safe usage, though it does not explicitly state when not to use it or point to alternatives such as bulk_upsert_identities.

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