diff --git a/.changes/22.enh.md b/.changes/22.enh.md
new file mode 100644
index 0000000..ac7ae60
--- /dev/null
+++ b/.changes/22.enh.md
@@ -0,0 +1 @@
+Every error now ends with how to fix it: an already checked-out branch points at `wt go`, config errors name both files the bad value could live in, unknown config keys and failing setup/refresh hooks say what to change, and a failed `wt sync` fast-forward lists the local commits in the way. (#22)
diff --git a/PLAN.md b/PLAN.md
index 9f128a9..fd354f1 100644
--- a/PLAN.md
+++ b/PLAN.md
@@ -783,7 +783,7 @@ stays short):
       (Homebrew cask detected through the PATH symlink;
       the rc file's actual eval lines quoted by line number).
 - [ ] End-to-end `brew uninstall` re-verification (needs the `v0.1.0` cask).
-- [ ] Failure-message audit: every error names the fix
+- [x] Failure-message audit: every error names the fix
       (`error: branch 'x' already checked out in ../acme.trees/x — wt go x?`).
 - [ ] Cut `v0.1.0` — the first real release:
       the cask publishes to the tap;
diff --git a/internal/cli/claim.go b/internal/cli/claim.go
index a3f3736..a3c7190 100644
--- a/internal/cli/claim.go
+++ b/internal/cli/claim.go
@@ -47,7 +47,8 @@ func runClaim(cmd *cobra.Command, branch, baseFlag string, noFetch bool) error {
 		return err
 	}
 	if t, ok := treeHoldingBranch(trees, branch); ok {
-		return preconditionf("branch %q is already checked out in %s", branch, t.Path)
+		return preconditionf(
+			"branch %q is already checked out in %s — `wt go %s` jumps there", branch, t.Path, branch)
 	}
 	if err := checkBase(ctx, p.g, base); err != nil {
 		return err
diff --git a/internal/cli/config.go b/internal/cli/config.go
index 0088095..c196cac 100644
--- a/internal/cli/config.go
+++ b/internal/cli/config.go
@@ -88,7 +88,7 @@ func runConfigEdit(cmd *cobra.Command) error {
 	edit.Stdout = os.Stdout
 	edit.Stderr = os.Stderr
 	if err := edit.Run(); err != nil {
-		return fmt.Errorf("editor %q: %w", editor, err)
+		return fmt.Errorf("editor %q: %w — set $VISUAL or $EDITOR to a working editor", editor, err)
 	}
 
 	// Validate right away: a typo surfaces now, at the terminal
diff --git a/internal/cli/copies.go b/internal/cli/copies.go
index 59a1003..ce34cc2 100644
--- a/internal/cli/copies.go
+++ b/internal/cli/copies.go
@@ -47,7 +47,7 @@ func copyFiles(
 			continue
 		}
 		if err != nil {
-			return fmt.Errorf("copy %s: %w", name, err)
+			return copyError(name, err)
 		}
 		fmt.Fprintf(chatter, "copy: %s\n", name)
 	}
@@ -147,7 +147,11 @@ func readCopy(root, name string) (data []byte, ok bool, err error) {
 		return nil, false, nil
 	}
 	if err != nil {
-		return nil, false, fmt.Errorf("copy %s: %w", name, err)
+		return nil, false, copyError(name, err)
 	}
 	return data, true, nil
 }
+
+func copyError(name string, err error) error {
+	return fmt.Errorf("copy %s: %w — fix the file, or drop it from copy in wt.toml", name, err)
+}
diff --git a/internal/cli/doctor.go b/internal/cli/doctor.go
index 1b9ed9f..7796e3b 100644
--- a/internal/cli/doctor.go
+++ b/internal/cli/doctor.go
@@ -109,7 +109,8 @@ func runDoctor(cmd *cobra.Command, info BuildInfo, jsonOut, offline bool) error
 	// No locational claim in the message: under --json the fixes are
 	// in the payload, not "above".
 	if view.Issues > 0 {
-		return preconditionf("%d %s found", view.Issues, plural(view.Issues, "issue"))
+		return preconditionf("%d %s found — each fix is listed above",
+			view.Issues, plural(view.Issues, "issue"))
 	}
 	return nil
 }
diff --git a/internal/cli/init.go b/internal/cli/init.go
index d63acee..da8d574 100644
--- a/internal/cli/init.go
+++ b/internal/cli/init.go
@@ -167,8 +167,7 @@ func provisionInitialPool(ctx context.Context, r *repo.Repo, chatter io.Writer)
 		// exists: a resize to the size already configured returns
 		// early, while every claim provisions what it finds missing.
 		return fmt.Errorf(
-			"%w — the config is saved; fix the cause (`wt config --edit` for hooks), "+
-				"and the missing slots provision on the next claim", err)
+			"%w; the config is saved, and the missing slots provision on the next claim", err)
 	}
 	return nil
 }
diff --git a/internal/cli/new.go b/internal/cli/new.go
index 5976c69..e1c728b 100644
--- a/internal/cli/new.go
+++ b/internal/cli/new.go
@@ -52,7 +52,8 @@ func runNew(cmd *cobra.Command, branch, baseFlag string, noFetch bool) error {
 		// R4: when the branch lives in some tree already,
 		// the error must point straight at it.
 		if t, ok := treeHoldingBranch(trees, branch); ok {
-			return preconditionf("branch %q is already checked out in %s", branch, t.Path)
+			return preconditionf("branch %q is already checked out in %s — `wt go %s` jumps there",
+				branch, t.Path, branch)
 		}
 		// In pool mode the natural resume for an existing branch,
 		// say one left by a claim that failed after its branch
diff --git a/internal/cli/root.go b/internal/cli/root.go
index 711c699..f1f896d 100644
--- a/internal/cli/root.go
+++ b/internal/cli/root.go
@@ -128,7 +128,7 @@ func runRoot(cmd *cobra.Command, _ []string) error {
 	err := runJump(cmd, "")
 	var notRepo *repo.NotARepoError
 	if errors.As(err, &notRepo) {
-		return fmt.Errorf("%w — `wt --help` shows usage", err)
+		return fmt.Errorf("%w; `wt --help` shows usage", err)
 	}
 	return err
 }
diff --git a/internal/cli/shellinit.go b/internal/cli/shellinit.go
index 91b23e2..b1e9eec 100644
--- a/internal/cli/shellinit.go
+++ b/internal/cli/shellinit.go
@@ -27,7 +27,7 @@ func newShellInitCmd() *cobra.Command {
 		Short: "Emit the shell integration for eval in ~/.zshrc",
 		Args: cobra.MatchAll(cobra.ExactArgs(1), func(_ *cobra.Command, args []string) error {
 			if args[0] != "zsh" {
-				return fmt.Errorf("unsupported shell %q — v1 supports zsh only", args[0])
+				return fmt.Errorf("unsupported shell %q — wt supports zsh only: `wt shell-init zsh`", args[0])
 			}
 			return nil
 		}),
diff --git a/internal/cli/slots.go b/internal/cli/slots.go
index 6c2cc8e..339bf1f 100644
--- a/internal/cli/slots.go
+++ b/internal/cli/slots.go
@@ -448,7 +448,8 @@ func (p *poolRepo) pinForRelease(
 	// lease reaches Repin as "expect nothing" without further ado.
 	held, err := lease.Get(leases, slot)
 	if err == nil && held == nil && claimRequired {
-		return nil, preconditionf("%s is not claimed — nothing to release", slot)
+		return nil, preconditionf(
+			"%s is not claimed — nothing to release; `wt pool ls` shows the claimed slots", slot)
 	}
 	pinned, err := lease.Repin(leases, slot, branch, held)
 	if err != nil {
diff --git a/internal/cli/sync.go b/internal/cli/sync.go
index ac0542d..9860eca 100644
--- a/internal/cli/sync.go
+++ b/internal/cli/sync.go
@@ -57,7 +57,8 @@ func runSync(cmd *cobra.Command, all bool) error {
 	}
 
 	if err := g.Fetch(ctx, remote); err != nil {
-		return fmt.Errorf("fetching %s: %w", remote, err)
+		return fmt.Errorf("fetching %s: %w — check `git remote -v` and your network, then rerun",
+			remote, err)
 	}
 	fmt.Fprintf(chatter, "fetched %s\n", remote)
 	// Best-effort: the fetch already succeeded, so a state-write
@@ -144,7 +145,8 @@ func fastForwardBase(
 	}
 	if ffErr != nil {
 		return preconditionf(
-			"%s could not fast-forward to %s (%v) — resolve it by hand", base, up, ffErr)
+			"%s could not fast-forward to %s (%v) — `git log %s..%s` lists the local commits "+
+				"in the way; move them to a branch, then rerun", base, up, ffErr, up, base)
 	}
 	fmt.Fprintf(chatter, "%s fast-forwarded %s to %s\n", base, commits(behind), up)
 	return nil
diff --git a/internal/cli/testdata/script/errors-name-fix.txtar b/internal/cli/testdata/script/errors-name-fix.txtar
new file mode 100644
index 0000000..3030c85
--- /dev/null
+++ b/internal/cli/testdata/script/errors-name-fix.txtar
@@ -0,0 +1,47 @@
+# Every error names its fix: the user should never have to guess
+# the next command. One case per family of failure.
+
+[!exec:git] skip 'git not on PATH'
+
+# outside a repository
+exitcode 4 wt ls
+stderr 'not inside a git repository — cd into one first'
+
+# unsupported shell
+exitcode 2 wt shell-init bash
+stderr 'wt supports zsh only: `wt shell-init zsh`'
+
+exec git init -q -b main acme
+cd acme
+exec git commit -q --allow-empty -m 'initial'
+exec wt init --yes
+
+# a branch already checked out points at the tree that holds it
+exec wt new feature/login
+exitcode 3 wt new feature/login
+stderr 'already checked out in .*feature-login — `wt go feature/login` jumps there'
+
+# an invalid config value names both files it could live in
+cp $WORK/bad-staleness.toml .git/wt.toml
+exitcode 1 wt config
+stderr 'staleness_hours must not be negative, got -1 — fix it in .*\.git[/\\]wt\.toml or '
+
+# an unknown key says what to do about it
+cp $WORK/unknown-key.toml .git/wt.toml
+exitcode 1 wt config
+stderr 'unknown key "colour" .* — remove it or fix its spelling'
+
+# a failing setup hook names the key to fix
+cp $WORK/bad-hook.toml .git/wt.toml
+! exec wt new feature/pay
+stderr 'setup hook failed: .* — fix hooks.setup with `wt config --edit`'
+
+-- bad-staleness.toml --
+staleness_hours = -1
+
+-- unknown-key.toml --
+colour = "auto"
+
+-- bad-hook.toml --
+[hooks]
+setup = "exit 7"
diff --git a/internal/cli/tree.go b/internal/cli/tree.go
index a777394..e8518ed 100644
--- a/internal/cli/tree.go
+++ b/internal/cli/tree.go
@@ -22,7 +22,8 @@ func resolveTree(ctx context.Context, trees []gitx.Worktree, name string) (gitx.
 		if t, ok := findTree(trees, top); ok {
 			return t, nil
 		}
-		return gitx.Worktree{}, fmt.Errorf("git does not list the current tree %s", top)
+		return gitx.Worktree{}, fmt.Errorf(
+			"git does not list the current tree %s — `git worktree repair` re-registers it", top)
 	}
 	// Every tree is a candidate here, bare entries included:
 	// exact-name commands may need to name states a jump never
diff --git a/internal/cli/warm.go b/internal/cli/warm.go
index 32cfcab..a53d2b7 100644
--- a/internal/cli/warm.go
+++ b/internal/cli/warm.go
@@ -38,7 +38,7 @@ func finishFresh(
 	}
 	fmt.Fprintf(chatter, "running setup hook: %s\n", setup)
 	if err := runHook(ctx, dest, setup, chatter); err != nil {
-		return fmt.Errorf("setup hook failed: %w", err)
+		return fmt.Errorf("setup hook failed: %w — fix hooks.setup with `wt config --edit`", err)
 	}
 	if files := cfg.Hooks.RefreshIfChanged; len(files) > 0 {
 		hash, err := pool.Hash(dest, files)
@@ -76,7 +76,7 @@ func refreshTree(
 	}
 	fmt.Fprintf(chatter, "running refresh hook: %s\n", refresh)
 	if err := runHook(ctx, dest, refresh, chatter); err != nil {
-		return fmt.Errorf("refresh hook failed: %w", err)
+		return fmt.Errorf("refresh hook failed: %w — fix hooks.refresh with `wt config --edit`", err)
 	}
 	if len(files) > 0 {
 		return st.WriteRefreshHash(name, current)
diff --git a/internal/config/config.go b/internal/config/config.go
index 4ca2dc8..4451277 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -119,7 +119,7 @@ func Load(globalPath, repoPath string) (Config, error) {
 	normalize(&cfg)
 
 	if err := validate(cfg); err != nil {
-		return Config{}, err
+		return Config{}, fmt.Errorf("%w — fix it in %s or %s", err, repoPath, globalPath)
 	}
 	return cfg, nil
 }
diff --git a/internal/config/load.go b/internal/config/load.go
index 50eff56..030adb7 100644
--- a/internal/config/load.go
+++ b/internal/config/load.go
@@ -57,7 +57,8 @@ func positionedError(path string, err error) error {
 		// beats a wall of positions.
 		e := strict.Errors[0]
 		row, col := e.Position()
-		return fmt.Errorf("%s:%d:%d: unknown key %q (not part of wt's config)",
+		return fmt.Errorf(
+			"%s:%d:%d: unknown key %q (not part of wt's config) — remove it or fix its spelling",
 			path, row, col, strings.Join(e.Key(), "."))
 	}
 	var decode *toml.DecodeError
diff --git a/internal/repo/repo.go b/internal/repo/repo.go
index 237864a..fc41365 100644
--- a/internal/repo/repo.go
+++ b/internal/repo/repo.go
@@ -43,7 +43,8 @@ func Find(ctx context.Context, dir string) (*Repo, error) {
 	common, bare := lines[0], lines[1] == "true"
 	if bare {
 		return nil, fmt.Errorf(
-			"%s is a bare repository; wt needs a main checkout to anchor config and trees", common)
+			"%s is a bare repository; wt needs a main checkout to anchor config and trees — "+
+				"run wt from a clone with a working tree", common)
 	}
 	if filepath.Base(common) == ".git" {
 		return &Repo{CommonDir: common, Root: filepath.Dir(common)}, nil
@@ -143,7 +144,7 @@ type NotARepoError struct {
 }
 
 func (e *NotARepoError) Error() string {
-	return fmt.Sprintf("%s is not inside a git repository", e.Dir)
+	return fmt.Sprintf("%s is not inside a git repository — cd into one first", e.Dir)
 }
 
 // WtExitCode maps to D13's "not a wt repo" contract code;