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

Annotations already indicate readOnlyHint=false and destructiveHint=false, so the basic write/safety profile is covered. The description adds meaningful behavioral context: it works only on simple accountless splits, and secure splits are read-only (a key constraint). It does not elaborate on reversibility or other side effects, but for a payment-recording tool with annotations present, the added constraint context justifies a 4.

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?

Three sentences, zero filler. It front-loads the core purpose, then the workflow hint, then the critical constraint. Every sentence earns its place with actionable information.

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 mutate-tool with full schema coverage, an output schema, and rich annotations, the description covers the essential points: what it does, the prerequisite workflow, the split-type constraint, and when it isn't applicable. The return value is handled by the output schema. Complex enough with 6 parameters, but schema + description together are sufficient.

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 baseline is 3. The description adds value by conveying the payment direction semantics ('who sent the money' vs 'who received it') and by clarifying the split types each field applies to. However, most parameter meaning is already well-documented in the schema's per-field descriptions, so the description's marginal parameter contribution is modest — a 4 reflects the useful direction-of-payment framing.

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 uses a specific verb+resource combination ('Record that one person paid another back, settling part or all of a debt') and clearly distinguishes from siblings by noting it works on simple, accountless splits while secure splits are read-only. It names a sibling ('get_split') to clarify workflow context.

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?

Provides explicit when-to-use guidance: 'Use get_split first to see who should pay whom' explains the prerequisite workflow. It also gives explicit exclusions — secure splits are read-only here and must be opened in a browser — which prevents misuse on the wrong split type. This is exemplary usage guidance.

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