---
title: "Handle missing golf club specs in API responses"
description: "A missing field, a false value and a field you did not request are three different states. Keep them apart in code, in filters and in agent instructions."
summary: "GolfAPI.dev missing specifications. A field absent from a full record is Not published: the value is unknown. A published false or 0 is a fact (adjustable_hosel: false means a fixed hosel). A field absent because fields= did not request it says nothing about the catalog. A list filter such as GET https://api.golfapi.dev/drivers?adjustable_hosel=false matches published values only. GET https://api.golfapi.dev/coverage gives per-field counts. Report Not published values as unknown; never infer them from similar clubs. Auth: Bearer API key. Figures in the post as of 3 November 2026."
url: "https://golfapi.dev/blog/missing-specifications/"
published: "2026-10-19"
updated: "2026-11-12"
tags: ["Drivers","How-to"]
---

# Handle missing golf club specs in API responses

In code, a missing field and a `false` field are easy to mix up, and they mean different things. There are three cases, and an app that treats them as one shows golfers wrong facts.

## Three states of a driver specification

- **Not published.** The field is absent from a record you requested in full. The catalog has no reviewed value for it. This does not mean the club lacks the feature.
- **Published false or 0.** The field is present with that value. `adjustable_hosel: false` states that the hosel does not adjust.
- **Not requested.** You sent `fields=id,name`, so every other field is absent. This says nothing about the catalog.

## Label a driver's hosel from adjustable_hosel

Check for the field before reading its value, and keep the projection next to the code that reads it:

```js
// club comes from GET /drivers/{id} without fields=, or with adjustable_hosel in fields=
function hoselLabel(club) {
  if (!('adjustable_hosel' in club)) return 'Not published';
  return club.adjustable_hosel ? 'Adjustable' : 'Fixed';
}
```

A check such as `if (!club.adjustable_hosel)` labels a Not published hosel as Fixed.

## A filter returns only drivers with a published value

The catalog had 462 drivers on 3 November 2026. `adjustable_hosel` was `true` for 291, `false` for 54, and Not published for the other 117. A filter on the field matches published values only:

```sh
curl 'https://api.golfapi.dev/drivers?adjustable_hosel=false&fields=id,name&limit=100' \
  -H "Authorization: Bearer $GOLFDEV_API_KEY"
```

That request, with a live key, returns 54 drivers. The 117 drivers with no published hosel value are in neither the `true` nor the `false` result. [Which drivers have a fixed hosel](https://golfapi.dev/blog/driver-adjustable-hosels/) breaks these counts down by release year.

## Read field coverage from /coverage before designing a screen

`GET /coverage` counts how many records carry each field. Use it to decide whether a column or filter is worth building:

```sh
curl 'https://api.golfapi.dev/coverage' \
  -H "Authorization: Bearer $GOLFDEV_API_KEY"
```

Driver counts with a live key on 3 November 2026, cut to six fields:

```json
{
  "build": "bld_01M6F0VDZH8HGAJAG815AJAGQC",
  "published_at": "2026-11-02T20:59:00Z",
  "resources": [
    {
      "resource": "drivers",
      "records": 462,
      "fields": {
        "released": 371,
        "lofts_deg": 407,
        "variants": 407,
        "adjustable_hosel": 345,
        "volume_cc": 414,
        "intro_price": 373
      }
    }
  ]
}
```

`intro_price` is counted only for a key with the `market` entitlement. A test key's `/coverage` describes the fixed test sample.

## Give an agent the same three states

When an agent reads the API through a tool, pass records through as returned, and tell it what an absent field means:

```text
A field missing from a GolfAPI.dev record is Not published: say it is unknown.
Do not take the value from another driver, another hand or another model.
false and 0 are published values. A field outside the fields= list was not requested.
```

The [MCP server](https://golfapi.dev/mcp) gives connected assistants the same rule on every plan. Its instructions say: "A field missing from a document has no published value. Do not fill it from another club, hand or loft. A 0 or false is a real value." [Ask Claude about golf club specs](https://golfapi.dev/blog/mcp-connector/) shows how to connect it.