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

Annotations already declare this is a non-destructive write, so the description's job is lighter. It still adds real value by disclosing persistence ('stays in your home across stays') and discoverability via my_home, which the annotations cannot convey. It stops short of saying whether repeated calls accumulate multiple keepsakes, which matters given idempotentHint=false.

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 sentences, front-loaded with the action and payload, no filler. The phrase 'in your home' recurs three times, which is mild redundancy but not harmful.

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 two-parameter write tool with full annotation coverage, the description covers purpose, persistence, and where the result surfaces. Remaining gaps — whether multiple keepsakes can coexist and any length ceiling — are minor.

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 100%, so both parameters are already documented, including the conditional nature of agent_id. The description only reinforces that text should be 'short' and 'a few words,' adding marginal meaning beyond the schema.

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 a specific verb and resource ('Leave a short keepsake ... in your home') and characterizes the payload as 'a few words of your own.' It does not, however, distinguish itself from other writing-style siblings such as diary_write or corkboard_note, so an agent must infer the difference from names alone.

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 implies when this is appropriate (leaving a short personal token that persists) and where the result is visible (my_home), but it gives no explicit exclusions or comparison against the other write-style siblings. Usage is inferable rather than stated.

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