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

Annotations only say readOnlyHint=false and openWorldHint=true; the description adds the exact price and chain ($0.25 USDC on Base, x402), that settlement happens before execution, the pre-check that refuses a doomed paid call, and the failure mode for wallets with no workspace. These are genuine behavioral facts an agent cannot get from the annotations or schema.

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?

Price and scope are front-loaded, which is good, but the pre-check rule is stated twice ('A free pre-check rejects a wallet with no workspace before any charge..' and '(a free check refuses a call that would fail)'), and there is a stray double period. Roughly a quarter of the text is redundant.

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-parameter paid mutation, the description covers price, settlement order, preconditions, and retry protocol, and no output schema exists to defer to. The remaining gap is the return value — it does not say whether the caller gets the new expiry timestamp, a receipt, or any confirmation.

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 schema has zero properties, so baseline is 4. The description goes further by documenting the out-of-band payment carrier params._meta["x402/payment"], which is not represented in the schema at all — a real addition, though the schema's additionalProperties:false makes that instruction appear inconsistent with the declared input contract.

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 states a specific verb (extend/renew) and two concrete resources: the workspace and the paying wallet's persistent key-value store, both for 30 days from the later of now or expiry. It is unmistakable against siblings (export/head/menu/read/write/snapshot_fetch), though the phrasing 'Extend the workspace... Agent memory: ...' leaves the relationship between the workspace and the KV store slightly implicit.

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 invocation flow: call once without payment to get the price, then retry with params._meta["x402/payment"]. It also states a precondition ('a free pre-check rejects a wallet with no workspace before any charge'). It stops short of stating when a caller should renew versus let a workspace lapse, but the payment protocol guidance is unusually actionable.

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