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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=false), and the description adds genuinely useful behavioral detail beyond them: value is null before the first logged value and carried_from marks days without their own value. With no output schema, this return-shape disclosure carries real weight.

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 compact sentences, front-loaded with the cardinality ('one value per day') before the null/carry semantics. No filler, though the semicolon-joined second clause is dense and slightly harder to parse than separate sentences.

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 two-parameter read tool with no output schema, the description covers the critical return semantics (daily granularity, null values, carried_from). It omits ordering, error behavior for an invalid tracker_id, and whether today's value can be partial, but nothing essential to correct invocation 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%, so both parameters (days, tracker_id) are already documented, including the 'up to and including today' semantics. The description's 'last N days up to today' restates the days parameter without adding format or edge-case detail, so baseline 3 applies.

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?

States the resource, granularity and scope explicitly: one value per day for the last N days up to today, tied to a tracker chart. It is clear what is returned and how it differs from raw entry data, though it never names the closest sibling get_entries, so an agent must infer that distinction.

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 phrase 'like the chart' hints this is the charting/aggregation endpoint, but there is no explicit when-to-use, when-not, or named alternative to get_entries. With seven siblings, the description leaves the agent to infer selection on its own.

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