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

Annotations provide only readOnlyHint=false, which is limited. The description adds meaningful behavioral detail: setting a value for a day, 0 clearing it, and no value meaning fully done. This goes beyond what the annotations alone convey, though it could also mention persistence/overwrite behavior more explicitly.

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?

Two short sentences carry the essential meaning without redundancy. The main action is front-loaded, and the edge cases (0 clears, no value = done) are included with minimal wording.

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 3-parameter write tool with no output schema, the description together with the schema and annotations covers what an agent needs to invoke it correctly. It could mention the result/return behavior or confirm overwrite semantics, but nothing essential is missing.

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%, and the schema already documents date format, value semantics, and the habit_id. The description reinforces the core value behavior but does not meaningfully add beyond the schema's parameter descriptions, so the baseline 3 is appropriate.

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 identifies the action ('Log a habit entry') and the target resource (a habit date entry), making it easy to distinguish from sibling logging tools like log_focus_session or log_workout. It also conveys the core semantics of setting a value for a day, which disambiguates it from get_daily_entry or update_daily_entry.

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 provides clear context for when the tool is used: logging a habit entry for a date, including how missing vs zero values behave. It does not explicitly name alternatives or state when not to use it, but the intent is sufficiently clear given the tool name and sibling set.

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