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

Beyond the annotations (readOnlyHint=false, destructiveHint=false, idempotentHint=false), it discloses two behaviors the agent could not infer: every successful update creates a new revision, and content is stored verbatim with no LLM rewriting unless the caller explicitly opts in. The content policy also flags a real compliance constraint. It does not describe what happens on a missing/invalid ID or the response shape, but that gap is modest.

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 target ID, then requirements, then revision semantics, then the policy block. The content-policy sentence is long but carries genuine safety value; there is little filler, though the requirement clause partially duplicates the schema.

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?

With an output schema present and full schema coverage, the description need not explain return values, and it covers the mutation semantics (revision creation) and the rewrite default that the schema only documents locally. It does not address failure modes for a non-existent or malformed mem-* ID, which is the remaining gap for a mutation tool.

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 explains target_id, rewrite, and every nested changes field in detail. The description only restates that at least one of content/headline/tags/metadata is required and adds the mem-* ID format; it says nothing about collection/collections or the rewrite flag, leaving the schema to do the work. 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?

"Update an existing memory in Maindex (Smart) by mem-* ID" gives a specific verb, resource, and targeting key, so the operation is unmistakable. It stops short of naming the siblings (keep/forget/recall) or stating that this is the mutation counterpart to them, so differentiation is inferred rather than explicit.

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 (modify a memory that already exists, at least one field required) and adds a strong when-NOT constraint in the content policy covering secrets and protected PII. It never names an alternative tool or states the condition that would send the agent to keep/forget/recall instead, so routing guidance is only implied.

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