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

Annotations already cover read-only, non-destructive and open-world behavior, and the description adds material context beyond them: per-call pricing ($0.01 via x402 USDC or card key), first 25 free, failed calls free, and that repeats are charged. That last point explains why idempotentHint=false on a pure read, resolving what would otherwise look like an inconsistency.

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?

Return contents and the mantle_gas routing decision are front-loaded in the first two sentences, with pricing appended afterwards. It is a single dense paragraph rather than a list, but no sentence is discardable given the pay-per-call model.

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?

Despite having no output schema, the description enumerates the returned fields in enough detail that an agent knows what it will get, and it covers cost and side-effect posture. Nothing needed to call this one-parameter tool correctly is missing.

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% and the single parameter already documents the 5-100 range and default of 20; the description only restates those bounds plus a trivial "Example: blocks=20". Baseline 3 applies since the schema carries the semantic load.

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 ("Gas price history on Mantle (eth_feeHistory)") and enumerates exactly what comes back: base fee in gwei per block, block fullness, 10th/50th/90th percentile priority fees, and low/avg/high base fee over the window. It is unambiguously distinguishable from the sibling mantle_gas, which it names.

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 concrete use cases (judge whether fees are rising, pick a priority fee, time a transaction) and an explicit exclusion rule: "for the current price alone use mantle_gas." The when-to-use and the alternative are both stated, leaving nothing to inference.

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