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

Annotations already declare readOnlyHint=false and idempotentHint=false, so the write/non-idempotent nature is known. The description adds substantial context beyond that: it is a paid builder (builder fee applies), it produces unsigned transactions requiring local signing, and the signer boundary (hosted builders never receive keypair bytes; value-moving results must be finalized locally). This is exactly the kind of operational behavior an agent needs before calling, so it earns a 4. Minor deduction only because the SAP execution guidance block is template-like and not tool-specific.

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 core purpose, scoping, and alternative are front-loaded in the first two sentences, which are efficient. The follow-up workflow and fee note are useful, and the execution guidance block is informative despite being boilerplate. It runs long (roughly 140 words) but every sentence earns its place; a small deduction for the length of the appended SAP guidance section that applies broadly.

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 complex 20-parameter, 7-required write builder with an output schema, the description is thorough: purpose, selection criteria, named alternative, feature support, follow-up transaction pipeline, pricing, and signer boundary are all covered. The 100% schema coverage and presence of an output schema relieve the description of documenting params and return shape. Nearly complete — only tool-specific failure modes beyond initVaultIfMissing go unmentioned.

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 — the schema already documents all 20 parameters including enum meanings for visibility/fromBalance/toBalance and the TRANSACTION_TOO_LARGE warning on initVaultIfMissing. The description adds only light value by linking features (delayed settlement, split transfers, gasless mode) to their corresponding parameters (maxDelayMs, split, gasless), but no syntax or format detail beyond the schema. Baseline 3 is correct.

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?

The description opens with a specific verb and resource: 'Build an unsigned SPL token transfer through an Ephemeral Rollup.' It then explicitly names the sibling it is not — sap_build_spl_transfer — and the exact condition (private visibility or ephemeral balance) that selects this tool. An agent can disambiguate it without opening any 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 an explicit when-to-use ('only when private visibility or an ephemeral balance is explicitly requested') and an explicit when-not-to-use with the named alternative ('For an ordinary public base-to-base wallet transfer, use sap_build_spl_transfer instead'). It also routes follow-up steps (sap_preview_transaction, sap_sign_transaction, sap_submit_signed_transaction, sap_payments_finalize_transaction). Nothing is left to inference.

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