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

Adds real context beyond the annotations: the return value is a shareable link, no signup is required for recipients, anyone with the link can edit, and a persisted page is created. It doesn't address what happens on repeated calls (a duplicate group?) despite idempotentHint=false, which would be the remaining useful disclosure.

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?

Front-loaded with the core use case and alternative routing, and everything included is relevant. The one-off distinction is stated three times in slightly different words ("not just a one-time calculation", "only call it when...", "For a one-off answer use halves_settle_up"), which is mild redundancy.

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 mutation tool with no output schema, the description supplies the missing return semantics (a link), the access model (anyone can open/edit, no signup), the persistence side effect, and the routing alternative. An agent has enough to call it correctly and to explain the outcome to a user.

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, but the worked example ({"name": "Lisbon trip", "currency": "EUR", "people": [...]}) makes the shape and intent of the parameters concrete in a way the schema alone does not. The optional `expenses` parameter is not mentioned in the description beyond the general concept of expenses.

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 concrete verb+resource (creates a group, returns a link) and immediately distinguishes the outcome from a one-time calculation by naming the sibling tool. An agent can tell this apart from halves_settle_up without opening either 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?

Explicit when-to-use (user wants a shared place to keep adding expenses and see who owes whom) and explicit when-not (one-off answer → use halves_settle_up). It also warns that only calling when a shared group is wanted matters because a saved page is created.

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