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

The annotations already flag the tool as non-read-only, destructive, and idempotent. The description adds valuable behavioral detail beyond those annotations: partial-update semantics, null-clearing for categoryId, merchant, and note, tag replacement behavior, and the cross-currency amount requirement. There is no contradiction with the 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?

Three short sentences, no filler, and the most important behavioral constraint—'Only the fields passed are changed'—is front-loaded. Every sentence earns its place by conveying information an agent needs to invoke the tool correctly.

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 an 11-parameter mutation tool with a rich output schema and safety annotations, the description covers the non-obvious semantics: partial updates, null clearing, tag replacement, ID source, and cross-currency handling. It does not discuss type-change limitations or explicitly route agents to add/delete siblings, but those are either inferable or visible in the schema.

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?

With 64% schema description coverage, the description compensates meaningfully by clarifying null semantics for parameters that lack full schema descriptions, such as merchant and note, and by stating the general partial-update contract. It also adds cross-currency context for amount and toAmount. Date and type rely on schema constraints, but those are reasonably self-explanatory.

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 opens with a specific verb and resource: 'Changes an existing transaction.' The qualifier 'existing' clearly separates this tool from add_transaction and delete_transaction, and the title 'Edit a transaction' reinforces the intent. An agent can confidently distinguish this tool without inspecting sibling schemas.

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?

The description provides clear context for use: only passed fields are changed, null clears specific fields, tagIds replaces all tags, transaction IDs come from list_transactions, and cross-currency moves require an amount in the destination currency. It does not explicitly name add_transaction or delete_transaction as alternatives, so it stops short of a full when-to-use instruction.

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