Update multiple ACF field values for a WordPress post in one call by specifying the site, post ID, and field name-value pairs.
Update multiple ACF field values for a post
| Name | Required | Description | Default |
|---|---|---|---|
| site | Yes | Site id (see list_sites) | |
| fields | Yes | Field name => value pairs | |
| post_id | Yes | Post ID |
Changes observed during successful MCP inspections.
v3.4.0Input schema / properties / siteAdded value: +{
+ "description": "Site id (see list_sites)",
+ "type": "string"
+}Input schema / requiredPrevious value: -[
- "post_id",
- "fields"
-]New value: +[
+ "site",
+ "post_id",
+ "fields"
+]v2.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full behavioral burden for a mutation tool. It does not say whether unspecified fields are preserved or overwritten, whether it requires auth, whether it fires hooks or creates revisions, or what it returns — all material for a write operation.
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?
A single efficient sentence with the verb and scope front-loaded and no wasted words. It is arguably under-specified rather than over-long.
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 nested-object mutation tool with no annotations and no output schema, the one-line description leaves key behaviors unexplained — merge vs replace semantics, permission needs, and error/return behavior. It should say more.
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%, with each parameter documented (site, post_id, fields) including a pointer to list_sites. The description adds no syntax or format guidance beyond the schema, so baseline 3 is appropriate.
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 (Update) and resource (ACF field values) scoped to a post, and the word 'multiple' distinguishes it from the singular sibling acf_update_post_field. It does not explicitly name that sibling, so it falls 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?
The description gives no when-to-use condition, no alternative tools, and no prerequisites. The only implied hint is the plural 'multiple', which suggests bulk updates, but the agent is left to infer when to pick this over acf_update_post_field.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.