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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds meaningful behavioral context: the return value is base64-encoded and must be decrypted client-side. This is exactly the kind of beyond-annotations disclosure that helps an agent handle the response correctly.

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?

Two short sentences, zero filler. The core action is front-loaded, and the critical return-format note is included without bloat.

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 simple read-by-slug tool with full schema coverage and safety annotations, the description is nearly complete. It could mention that the slug must exist or what happens on a miss, but the schema's pattern and the read-only annotations cover most of what an agent needs.

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 schema already documents both parameters. The description adds the fact that the blob is base64 and client-decrypted, which relates to the return value rather than the parameters. Baseline 3 is appropriate since the schema carries the parameter documentation burden.

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 states a specific verb ('Fetch') and resource ('journal blob by slug'), and the sibling list includes vigil_journal_list and vigil_journal_put, so the agent can distinguish this as the read-by-slug operation. It doesn't explicitly contrast with siblings, but the verb+resource is clear enough.

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 implies usage: call this when you need a journal blob by slug. It doesn't explicitly say when not to use it or mention alternatives like vigil_journal_list for enumeration. The sibling list provides context, but the description itself gives no routing guidance.

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