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 CrestApps/CrestApps.AgentSkills --skill crestapps-core-context-buildersgit clone --depth 1 https://github.com/CrestApps/CrestApps.AgentSkillsWrote 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/crestapps/crestapps.agentskills/crestapps-core-context-builders)<a href="https://agentmods.dev/skills/crestapps/crestapps.agentskills/crestapps-core-context-builders"><img src="https://agentmods.dev/badge/skills/crestapps/crestapps.agentskills/crestapps-core-context-builders/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/crestapps/crestapps.agentskills/crestapps-core-context-builders"><img src="https://agentmods.dev/badge/skills/crestapps/crestapps.agentskills/crestapps-core-context-builders.svg" alt="Reviewed on agentmods" width="80" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00175 | $0.01825 |
| Opus 5.5 | $0.00070 | $0.00730 |
| Sonnet 5.5 | $0.00035 | $0.00365 |
| Haiku 4.5 | $0.00017 | $0.00183 |
Grade A, and why
crestapps-core-context-builders 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 yesterday.
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 — 163 lines — stays where its author put it; the contents beside it link to each section on GitHub.
CrestApps.Core Context Builders
Two handler pipelines prepare every AI request:
| Level | Builder | Handler | Produces |
|---|---|---|---|
| Completion | IAICompletionContextBuilder.BuildAsync(resource, configure, cancellationToken) |
IAICompletionContextBuilderHandler |
AICompletionContext (deployments, system message, tools, agents, model parameters, data source) |
| Orchestration | IOrchestrationContextBuilder.BuildAsync(resource, configure, cancellationToken) |
IOrchestrationContextBuilderHandler |
OrchestrationContext (user message, history, documents, SystemMessageBuilder, completion context) |
Guidelines
- Use a completion handler for anything every completion of a resource needs, including non-orchestrated calls and sub-agents. Use an orchestration handler for work that only belongs to orchestrated chat.
- Both builders run
BuildingAsyncon every handler, then the caller'sconfiguredelegate, thenBuiltAsyncon every handler. - Handlers run in reverse registration order: the last registered runs first. Register an override after the handler whose values it replaces.
- A handler that throws (other than cancellation) is logged and skipped, and the build continues. A failing built-in handler can leave a profile without its system message, model parameters, tools and agents, so watch for "Error in completion context building handler" in logs.
- Completion handler methods have no
CancellationToken; orchestration handler methods take an optional one. - Pattern-match
Resource(AIProfile,ChatInteraction, or your own type) instead of assuming one resource type.
Built-in Handlers
| Completion handler | Adds |
|---|---|
AIProfileCompletionContextBuilderHandler |
Profile system message, sampling, deployments, prompt templates, tools, agents, chat and utility model parameters |
ChatInteractionCompletionContextBuilderHandler |
The same for a ChatInteraction |
AIPersonaCompletionContextBuilderHandler |
In BuiltAsync, prepends the linked persona block and stores it under AICompletionContextKeys.Persona (when personas are enabled) |
AIToolInstanceCompletionContextBuilderHandler |
ToolInstanceNames from AIToolInstanceMetadata (when tool instances are enabled) |
DataSourceAICompletionContextBuilderHandler |
The selected data source id |
McpAICompletionContextBuilderHandler |
MCP connection ids (when MCP is enabled) |
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.
- yesterday Changed · +59 lines · +153 tokens per session 04e2d92e25e9
- 1mo ago First seen · 104 lines · 22 tokens per session scan A 0cc00c66c3f9
crestapps-core-context-builders is a skill published in the GitHub repository CrestApps/CrestApps.AgentSkills (13 stars, last pushed yesterday), licensed MIT. It adds 175 tokens to every session and 1,825 once invoked, about $0.0007 per session on Opus 5.5. 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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