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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description still adds real context beyond that: the retention-boundary concept, the fact that no RPC endpoint exists so this MCP surface is the only read path, and that it emits an 'honesty note'. It stops short of describing error behavior for unknown chains, so not a full 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?

Front-loaded with the payload summary, then cleanly labeled 'When to use', 'Do not use', 'Returns', and 'Key fact'. Every sentence carries distinct information and none is redundant with the name or annotations.

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?

There is no output schema, and the description compensates by enumerating the returned row fields (chain, tier, name, client, state, capability) plus fee models and an honesty note. Combined with the clear usage triggers, an agent has what it needs to call and interpret this correctly.

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?

The tool takes zero parameters, so there is no parameter surface to document; the baseline for a no-param tool is 4. The description correctly implies the call needs no arguments by presenting the result as a whole-surface inventory.

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 resource and scope: per-chain capability, retention boundary, and fee model. It distinguishes itself from the nearest sibling by naming chain_status as the tool for live numbers, so an agent can route without opening the schema.

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?

Gives explicit when-to-use ('before promising that some query is possible', 'when a tool refused a query as out of range') and an explicit do-not-use with the alternative named ('for live numbers - that is chain_status'). Both the trigger and the exclusion are stated, not implied.

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