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

Annotations only tell the agent readOnlyHint=false and that it is non-idempotent/non-destructive; the description goes well beyond that by disclosing return fields, the timing rule against calling before a buy, how paid top-ups are credited, the session-cap/reset semantics, and the paymentsPaused/retryAfter behavior when Lightning is paused.

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?

It is front-loaded with the tool's purpose and every sentence carries operational content, but the run of short declarative clauses makes it feel like a list rather than a tight narrative, and some field enumeration is padded.

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 zero-required-parameter tool with a full output schema, the description covers usage timing, mutation side effects, and the paused-payment edge case. It re-explains return fields that the output schema already owns and does not clarify how the optional mutations compose with a plain balance check.

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 reset_session, issue_link_code, and session_budget_sats thoroughly. The description largely restates those same semantics (session cap, new session, one-time code) rather than adding new parameter meaning, so it sits at the baseline for full-coverage schemas.

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 clearly states the resource and its payload (remaining sats, hourly buy limit, plus the maxBuysPerHour/remainingBuysHour fields), so an agent understands it retrieves account balance state. It does not, however, contrast itself with nearby siblings such as spend_summary or top_up, which also deal with sats.

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 gives an explicit exclusion ('Do not call this before buying') and conditions for the optional mutations ('Set issue_link_code only when the human asks for a one-time sign-in code'), plus explains how top-ups are credited. It stops short of naming alternative tools for adjacent needs, so it is strong but not fully routing.

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