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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, so the safety bar is covered; the description adds genuinely new context: pricing (free), error contract (isError with message for invalid input or upstream failure, not charged), and the measurement basis for peg_deviation_pct. It stops short of describing pagination or freshness/update cadence.

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?

The lead sentence front-loads the payload (supply, change, price, peg deviation), followed by source, filter axes, the peg_deviation definition, and cost/error notes. Dense but each clause carries information; only the 'Filter by symbol or peg type' line is redundant with the schema.

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?

With an output schema present, return values need not be enumerated, and the description still clarifies peg_deviation_pct's measurement basis. Cost and error behavior are covered, leaving only minor gaps such as data freshness and whether the 1d/7d/30d windows are fixed.

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 the schema already documents peg, limit, and symbol with defaults, ranges, and enum values. The description only repeats 'filter by symbol or peg type' and adds no format or edge-case detail beyond that baseline.

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 concrete deliverables — circulating supply, 1d/7d/30d supply change, price, peg deviation, depegs, mint/burn flows — plus the data source (DefiLlama) and chain scope. It is immediately separable from siblings like crypto_price or defi_protocol, which cover price quotes and protocol TVL rather than stablecoin supply/peg data.

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?

It hints at filtering by symbol or peg type, which tells the agent the two selection axes, but never states when to prefer this over crypto_price or defi_rankings, nor any prerequisites. Usage is implied rather than prescribed, so it sits at the minimum-viable level.

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