List sources

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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint=false, so the description's added value is what it says about the payload: freshness timestamps, that 'tool' names the corresponding transaction tool, and an explicit prompt-injection warning that last_error is untrusted text. That last note is genuinely useful safety context an agent could not infer from schema or annotations. It stops short of describing volume, ordering, or auth requirements, so not a 5.

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, front-loaded with the purpose, then the usage trigger, then the field semantics and safety caveat. No sentence is redundant and nothing is buried.

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?

No arguments to explain, an output schema covers the return shape, and annotations cover the safety profile. The description fills the remaining gaps — why to call it, what 'tool' means, and the untrusted-text caveat — so an agent has everything needed to invoke and use it correctly.

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 tool takes zero parameters, so there is nothing for the description to disambiguate; baseline applies. The description instead spends its words on return-field semantics, which is the right allocation.

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 specific verb and resource ('List data sources') plus the distinguishing payload ('sync freshness (last_success_at, last_error)'). This is unmistakably different from the sibling transaction-fetching tools, which return transaction records rather than source-level sync metadata.

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?

'Check this to warn the user when data may be stale' gives a clear triggering condition for calling the tool, which is the main ambiguity for a no-arg listing tool. It does not state when not to call it or name an alternative, but the sibling set is transaction-oriented so the exclusion is implicit.

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