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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered externally. The description adds nothing beyond that – no note on what the returned plan contains, whether it mixes sessions/tasks/milestones, or how empty days behave.

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?

It is a single fragment with zero waste and the default is front-loaded, which is efficient. However, terse under-specification is not the same as good conciseness; the sentence omits the verb and any structure, leaning on the title to carry meaning.

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 retrieval tool with no output schema, the description should convey at least roughly what a 'plan' object is (items, sessions, goals) and whether an absent day returns empty or an error. None of that is present, leaving the agent able to call it but not to know what it will get back.

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% for the single date parameter, which already documents the YYYY-MM-DD format and user-timezone semantics. The description's '(default today)' adds the default behavior that the schema omits, but that is a marginal increment, so the 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?

The description is a noun phrase, 'The plan for a day (default today)', with no verb, but it does identify the resource (the day's plan) and a scope. It does nothing to distinguish itself from close siblings like get_planning_context, next_steps, get_commitments, or get_routines, so an agent must guess which retrieval tool it wants.

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 parenthetical '(default today)' hints that the date can be omitted, which is mild usage guidance. There is no statement of when to prefer this over the other plan/context/goal readers in the sibling list, and no exclusions or prerequisites.

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