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

Annotations already flag destructiveHint=true and readOnlyHint=false, and the description adds substantial context beyond that: replace wipes the branch's rows while uncovered periods keep prior values, merge upserts cell by cell, dry_run returns impact without persisting, a version is persisted and labelled with summary, and the tool is not advertised to read-only keys. That is exactly the destruction/scope/permission detail an agent needs on a mutation tool.

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?

Every sentence carries information - source exclusivity, timeline_ref rules, materialization, replace/merge/dry_run, return fields - and the core action is front-loaded. It is delivered as one very long paragraph however, and the lack of any break between the source discussion and the write-mode discussion makes it harder to scan than it needs to be for a 13-parameter tool.

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 no output schema, the description correctly enumerates the return payload (dataset_id, created_items, matched_items, entries_written, inputs_written, inputs_removed, warnings, plus file-path-only fields), which is the right use of the space. Auth behavior and version persistence are also covered; the main omission is replace_scope, which is an enumerated parameter left unexplained in both description and 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?

Schema description coverage is only 38% across 13 parameters, but the description compensates heavily, explaining branch.id/display_name/actuals_through, entries[] resolution via item_uid/item_label, entry_uid/entry_label list-mode targeting, timeline_ref grain constraints, file_id, sheet_name, structure_override, replace_source_id, and record_import. Gaps remain: replace_scope ('branch' vs 'import'), branch.priority, branch.source_hint, and branch.file_name are never explained.

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 first clause names a specific verb and resource ('Writes values onto a branch of the model') and immediately clarifies the create-if-absent behavior, so the agent knows exactly what the tool does. It does not, however, name or distinguish itself from close siblings such as layerz_parse_file, layerz_patch, or layerz_validate_model, so the routing value stops short of a 5.

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?

Mode selection is well covered: 'Two sources, mutually exclusive' explains when to use entries[] vs file_id, and the description explains when replace, merge, and dry_run apply and what each does. What is missing is guidance on choosing this tool over sibling tools (e.g. layerz_parse_file for inspection, layerz_validate_model for checks), so there are no explicit alternatives or exclusions.

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