add_hydration_data

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

Annotations declare readOnlyHint=false, destructiveHint=false and openWorldHint=true, so the safety profile is partly covered; the description adds genuinely new behavior: the 10000 magnitude cap, acceptance of negative values, and, most importantly, that the write is irreversible because no delete endpoint exists. It stops short of covering auth requirements, whether an existing same-timestamp entry is overwritten, or what a success response contains.

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?

Very short with no filler, and the most consequential fact (not round-trippable) is bolded for salience. The telegraphic fragment style with semicolons is somewhat clipped and reads as a note rather than a front-loaded sentence, which costs it a point but not much.

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 with no output schema, the description covers value semantics and irreversibility, which is the critical gap. It does not say what happens on a duplicate timestamp, whether a device/source is implied, or what the call returns, leaving the agent with partial 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 coverage is 67%: 'when' and 'cdate' are documented in the schema, but the required 'valueInMl' has no description at all. The description fills exactly that hole by specifying units (raw milliliters), the accepted magnitude range, and that negatives are legal — meaning the agent does not need to guess the unit or bounds for the only required parameter.

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 never states what the tool does; it is a fragment of constraint notes ('raw milliliters, magnitude capped at 10000, negative values allowed') with no verb+resource sentence. The agent must infer the purpose ('log a hydration entry') entirely from the tool name and the sibling pair get_hydration_data/add_hydration_data. Adequate in combination with the name, but the description itself contributes no purpose statement.

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?

There is no explicit when-to-use or when-not-to-use guidance versus siblings such as add_weigh_in or add_body_composition. The one operational caveat given — 'no delete endpoint exists, so not safely round-trippable' — implicitly warns the agent that this write cannot be undone, which is useful decision context, but it is not framed as usage guidance.

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