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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint=false, so the safety profile is covered; the description usefully confirms 'Nothing is signed or broadcast' and adds operational context absent from annotations (paid per call, 5 sats or US$0.005 USDC) plus a caveat that fee/fee-rate appear only when input data is present. It does not describe response shape, latency, or failure modes (e.g., malformed base64), so the addition is real but modest against already-rich annotations.

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?

Two sentences, front-loaded with the core action and followed by the payment/price note; very little waste. The first sentence crams six outputs into one comma-separated list, slightly reducing scannability, but nothing is extraneous.

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 no output schema, the description carries the return-content burden and does so by enumerating the decoded fields and the 'next step' guidance. Combined with the read-only annotations and explicit payment model, an agent has enough to call it correctly; only error handling and output formatting remain unspecified.

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 explains psbt (base64, URL-encode + as %2B), l402 token format, and the pay_with enum. The description only echoes '(base64)' and adds nothing about l402 or pay_with, which is acceptable given the schema covers them, hence the baseline 3.

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 gives a specific verb pair ('Decode and analyze') and a precisely named resource ('PSBT (base64)'), and enumerates what the analysis yields: inputs, outputs, fee and fee rate, estimated vsize, missing signatures, and next step. The PSBT resource implicitly distinguishes this from siblings such as bitcoin_decode_transaction and bitcoin_decode_script, but it never names those siblings, so the differentiation is left to inference.

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?

Usage is implied rather than stated: an agent can infer it should call this when it holds a base64 PSBT and wants inspection without signing. There is no explicit when-not guidance, no mention of when to prefer bitcoin_decode_transaction or plan_cpfp, and no prerequisites beyond the payment note.

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