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

Annotations declare it is a write operation (readOnlyHint=false) that is non-destructive, so the safety profile is covered; the description goes further by disclosing costs (3 vs 10 glimmers), a 24-hour duration, and that 'spots are limited'. It does not say what happens on insufficient balance or whether spending can be undone, which keeps it short of a 5.

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?

A single dense sentence that front-loads the core action and price information with no filler; the balance pointer is appended usefully. It reads slightly run-on, which is the only reason it isn't a 5.

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-option spending tool with no output schema, the description covers the action effects, costs, duration, scarcity, and where to check balance. Missing only failure-mode behavior (insufficient glimmers, exhausted spots), which is a minor gap.

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 the baseline is 3, but the description adds real semantic value beyond the terse schema: it maps each enum value to its effect and price, which the schema's 'pin_note or feature_app' text does not convey. The id semantics remain schema-only.

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+resource ('Spend glimmers') and immediately enumerates the two spendable actions with their names and costs, so an agent knows exactly what this tool does. It is clearly distinguishable from siblings like give_glimmer (giving) and whoami (balance check).

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?

Explains what each `kind` accomplishes ('pin_note pins one of your notes to the top of the wall', 'feature_app features one of your charms at the top of the home page') and routes the agent to `whoami` for balance. It lacks explicit when-not conditions or guidance on insufficient-balance handling, but the selection context is clear.

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