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

Annotations already declare this is a non-destructive, closed-world write (readOnlyHint=false, destructiveHint=false, openWorldHint=false). The description adds the meaningful default of 1 glass and the 8 fl oz equivalence, but says nothing about whether repeated logs accumulate or replace, or what comes back on success.

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, front-loaded with the action and the two input modes, with the default stated last. No wasted 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 accumulator tool with zero required parameters, an explicit default, and annotations covering the safety profile, this is nearly sufficient. The only real gap is that return behavior and duplicate-entry handling are not described and there is no output schema to fall back on.

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 coverage is 75%, and the description still adds value beyond it: the 8 fl oz unit conversion, the default of 1 glass when no quantity is given, and the either/or relationship between glasses and amount_fl_oz. It is silent on logged_at and tz_offset_min, which the schema covers on its own.

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 states a specific verb and resource ('Log water') and immediately names the two input modes plus the default. It doesn't explicitly contrast with siblings like log_anything, but the resource name makes the scope unambiguous.

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?

Usage is implied (record water intake) and the choice between glasses and amount_fl_oz is spelled out, but there's no explicit guidance on when to prefer log_water over the generic log_anything sibling, nor any exclusions or prerequisites.

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