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

Annotations only say readOnlyHint=true, so the description carries the return contract itself: 'created' vs 'updated' vs 'unchanged', and that unchanged is the typical outcome of a repeat run. It also discloses the no-op behavior when no sender is configured, which is the kind of state an agent could otherwise misread as a failure.

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 action and purpose, then the return shape, then the edge case. Dense and mostly waste-free, though the quoted key enumeration makes it heavier than it needs to be for a tool with one parameter.

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 output schema exists, and the description compensates by naming each result bucket and what `issues` contains ('newest first, so the summary can be written from it without another call'). Combined with the empty-state handling, an agent has everything needed to call and interpret this 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?

There is a single parameter with 100% schema coverage, and the schema already explains the default lookback (back to the last saved issue, up to 30 days). The description adds no syntax, format, or interaction detail beyond that, so baseline 3 applies.

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 ('Read every new issue from the allowed publications into the brain') and adds the downstream purpose ('so they can answer questions later'). An agent can distinguish it from find_my_newsletters and get_substack_reading without opening any 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?

Explicitly routes the empty case to a sibling: 'With no allowed sender it reads nothing and says so... call find_my_newsletters and ask.' It also frames the second-run-in-a-day scenario as normal, which tells the agent not to treat it as an error. Missing only a general 'use this instead of X when...' statement covering the happy path.

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