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

Annotations already define the tool as non-read-only, non-idempotent, and non-destructive, so the description only adds the behavior of accepting flexible time formats. This does not contradict annotations but adds only minimal context. No safety-relevant behaviors such as side effects or error handling are disclosed beyond the schema.

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 two sentences with no waste: the first sentence states the primary action and target, and the second adds a useful note about timestamp flexibility. It is front-loaded and appropriately sized for the tool's simplicity.

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 a complete schema, output schema, and annotations, the description is sufficient for an agent to understand the tool's operation. The only minor gap is the lack of explicit note about the entry being persisted or any prerequisites, but the structured fields cover the essential details. For a simple create tool, this is highly complete.

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%, meaning each parameter (babyId, timestamp, text, tags) has a clear description. The description's mention of flexible time formats merely echoes the timestamp parameter's existing schema description, adding no new semantic meaning. Baseline of 3 is appropriate for high schema coverage.

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 uses a specific verb ("Log") and identifies the resource ("diary/journal entry for a baby"), clearly distinguishing it from sibling tools like create_feed, create_nappy, and create_sleep. The title and description align perfectly to convey the tool's unique purpose.

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 implies when to use the tool (i.e., logging a diary/journal entry) but provides no explicit guidance on when to choose it over alternatives such as create_feed or create_sleep. No exclusions or alternative tools are mentioned, so the usage scenario is inferred rather than stated.

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