Mention the projection tooling in the projections docs

docs/server/features/projections/custom.md

@@ -33,6 +33,11 @@ fromStream('account-1')
     .outputState()
 ```
 
+::: tip
+Kurrent's [gaffer](https://gaffer.kurrent.io) tooling runs projections like this one on your machine and
+deploys them to a server.
+:::
+
 ## Projections API
 
 Below, you can find the JavaScript API for user defined projections.
@@ -111,9 +116,8 @@ handler. The event provided through the handler contains the following propertie
 
 ## Debugging
 
-User projections have a bonus that debugging is easier
-via any browser that ships with debugging capabilities. The screenshots in this document show the use of
-Chrome, but we have tested debugging with all major browsers including Firefox, Edge and Safari.
+A projection can log from inside a handler, and you can step through one before it goes anywhere near a
+server. Both are covered below.
 
 ### Logging from a projection
 
@@ -178,10 +182,13 @@ V2 is a parallel-partitioned engine with an incompatible checkpoint format and a
 Before selecting it, read [Projections Engine V2](./engine-v2.md) — in particular, V2 does not emit
 `outputState()` result streams and does not support `trackemittedstreams`.
 
-### Debugging projections
+### Stepping through a projection
 
-To develop and debug projections, use [Gaffer](https://github.com/kurrent-io/gaffer) — a standalone tool
-for authoring, running, and stepping through KurrentDB projections.
+The [gaffer](https://gaffer.kurrent.io) command line runs a projection on your machine with a debugger
+attached, against a file of sample events or against one of your databases, so you can set breakpoints,
+step through a handler and inspect the state as it changes without deploying anything. The
+[VS Code extension](https://gaffer.kurrent.io/extension/vs-code/) drives it from the editor, and any
+DAP-aware editor can attach to it.
 
 ## Configuring projections
 

docs/server/features/projections/intro.md

@@ -48,8 +48,8 @@ meet the criteria. The output of all queries is a stream, you can listen to this
 There are two types of projections in KurrentDB:
 
 - [Built in (system) projections](system.md)
-- [User-defined JavaScript projections](custom.md) which you create via the API or the admin
-  UI
+- [User-defined JavaScript projections](custom.md), which you write yourself and create through the
+  API, a client library, or the embedded UI
 
 ## Engine versions
 
@@ -58,6 +58,20 @@ KurrentDB ships two projection execution engines. V1 is the default. V2 is opt-i
 checkpoint format and omits some V1 features (notably `outputState()` result streams and
 `trackemittedstreams`). See [Projections Engine V2](./engine-v2.md).
 
+## Tooling
+
+Kurrent maintains tooling for developing user-defined projections:
+
+- **[gaffer](https://gaffer.kurrent.io)**, a command-line tool, runs a projection on your machine against
+  a file of sample events or subscribed to one of your databases. It deploys the projection to a server
+  when you are ready, and can run it with a debugger attached so you can step through a handler and watch
+  the state change. See [Your first projection](https://gaffer.kurrent.io/getting-started/first-projection/).
+- **[The VS Code extension](https://gaffer.kurrent.io/extension/vs-code/)** drives the same runs and
+  breakpoints from the editor, and shows which of your projections are deployed where. Other DAP-aware
+  editors can attach to the debugger too.
+- **[The testing library](https://gaffer.kurrent.io/testing/nodejs/)** feeds events to a projection from
+  a JavaScript test suite and hands back the state at each step for your tests to assert on.
+
 ## Performance impact
 
 Keep in mind that all projections emit events as a reaction to events that they process. We call this effect _write amplification_