Getting it into your agent
One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.
npx skills add christian289/dotnet-with-claudecode --skill optimizing-fast-lookupgit clone --depth 1 https://github.com/christian289/dotnet-with-claudecodeWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/skills/christian289/dotnet-with-claudecode/optimizing-fast-lookup)<a href="https://agentmods.dev/skills/christian289/dotnet-with-claudecode/optimizing-fast-lookup"><img src="https://agentmods.dev/badge/skills/christian289/dotnet-with-claudecode/optimizing-fast-lookup/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/skills/christian289/dotnet-with-claudecode/optimizing-fast-lookup"><img src="https://agentmods.dev/badge/skills/christian289/dotnet-with-claudecode/optimizing-fast-lookup.svg" alt="Reviewed on agentmods" width="80" height="20"></a>What it costs to keep this loaded
Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.00034 | $0.00652 |
| Opus 5 | $0.00017 | $0.00326 |
| Sonnet 5 | $0.00007 | $0.00130 |
| Haiku 4.5 | $0.00003 | $0.00065 |
Grade A, and why
optimizing-fast-lookup scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 10d ago.
A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.
Nothing flagged
None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.
How it starts
The opening of the file, as written. The whole thing — 108 lines — stays where its author put it; the contents beside it link to each section on GitHub.
.NET Fast Lookup
A guide for fast lookup APIs leveraging O(1) time complexity.
Quick Reference: See QUICKREF.md for essential patterns at a glance.
1. Core APIs
| API | Time Complexity | Features |
|---|---|---|
HashSet<T> |
O(1) | Mutable, no duplicates |
FrozenSet<T> |
O(1) | Immutable, .NET 8+ |
Dictionary<K,V> |
O(1) | Mutable, Key-Value |
FrozenDictionary<K,V> |
O(1) | Immutable, .NET 8+ |
2. HashSet
// O(1) time complexity for existence check
var allowedIds = new HashSet<int> { 1, 2, 3, 4, 5 };
if (allowedIds.Contains(userId))
{
// Allowed user
}
// Set operations
setA.IntersectWith(setB); // Intersection
setA.UnionWith(setB); // Union
setA.ExceptWith(setB); // Difference
3. FrozenSet (.NET 8+)
using System.Collections.Frozen;
// Immutable fast lookup (read-only scenarios)
var allowedExtensions = new[] { ".jpg", ".png", ".gif" }
.ToFrozenSet(StringComparer.OrdinalIgnoreCase);
if (allowedExtensions.Contains(fileExtension))
{
// Allowed extension
}
4. Dictionary<K,V> Optimization
// ❌ Two lookups
if (dict.ContainsKey(key))
{
var value = dict[key];
}
// ✅ Single lookup
if (dict.TryGetValue(key, out var value))
{
// Use value
}
// Lookup with default value
var value = dict.GetValueOrDefault(key, defaultValue);
5. Comparer Optimization
// Case-insensitive string comparison
var set = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
set.Add("Hello");
set.Contains("HELLO"); // true
6. When to Use
| Scenario | Recommended Collection |
|---|---|
| Frequently modified set | HashSet<T> |
| Read-only configuration data | FrozenSet<T> |
| Frequent existence checks | HashSet<T> / FrozenSet<T> |
| Key-Value cache | Dictionary<K,V> |
| Static mapping table | FrozenDictionary<K,V> |
7. References
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
What this file has done since we first saw it
Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.
- 10d ago First seen · 108 lines · 34 tokens per session scan A d9d400bdddd9
optimizing-fast-lookup is a skill published in the GitHub repository christian289/dotnet-with-claudecode (41 stars, last pushed 1mo ago), licensed MIT. It adds 34 tokens to every session and 652 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
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